# Yellow signs with three digits - what are they? **URL:** \ **Category:** Factual Questions\ **Created:** [May 8, 2014, 8:36pm UTC](https://boards.straightdope.com/t/yellow-signs-with-three-digits-what-are-they/688005 "2014-05-08T20:36:52Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![That\_Don\_Guy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/that_don_guy/32/538_2.png) [@That\_Don\_Guy](https://boards.straightdope.com/u/That_Don_Guy)\ **Post date:** [May 8, 2014, 8:36pm UTC](https://boards.straightdope.com/t/yellow-signs-with-three-digits-what-are-they/688005/1 "2014-05-08T20:36:52Z")
I have seen a few poles that have two identical signs, facing opposite directions and at an angle (as if they were meant to be seen from altitude). Each sign has three digits, with the third as a superscript as if the number was meant to be from 0.0 to 99.9. One sign is pretty much at the end of an airport runway, and another is about 10 miles north and could be aligned so that a plane going to/from that same runway could see it, so it’s possible that it has something to do with that, although I can’t find any reference to runway distance/direction signs that look like that anywhere. ---
**Author:** ![Keeve](https://avatars.discourse-cdn.com/v4/letter/k/f07891/32.png) [@Keeve](https://boards.straightdope.com/u/Keeve)\ **Post date:** [May 8, 2014, 8:40pm UTC](https://boards.straightdope.com/t/yellow-signs-with-three-digits-what-are-they/688005/2 "2014-05-08T20:40:55Z")
How big is the sign? It would have to be pretty big for a pilot to see it in flight. Can you find an example on Google maps so we can see what you mean? ---
**Author:** ![Senegoid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/senegoid/32/6606_2.png) [@Senegoid](https://boards.straightdope.com/u/Senegoid)\ **Post date:** [May 8, 2014, 8:57pm UTC](https://boards.straightdope.com/t/yellow-signs-with-three-digits-what-are-they/688005/3 "2014-05-08T20:57:14Z")
I see signs somewhat like that in a lot of places, often along rural or semi-rural roads. In general, I have no idea if there are airports anywhere around. They do look like they are intended to be viewed from an aircraft, but they don’t look like any serious kind of navigation aid. I wonder if they are some kind of surveying marker. ---
**Author:** ![StrangerThanFiction](https://avatars.discourse-cdn.com/v4/letter/s/f05b48/32.png) [@StrangerThanFiction](https://boards.straightdope.com/u/StrangerThanFiction)\ **Post date:** [May 8, 2014, 9:35pm UTC](https://boards.straightdope.com/t/yellow-signs-with-three-digits-what-are-they/688005/4 "2014-05-08T21:35:58Z")
Aerial pipeline marker? > **[Vulcan Utility Signs - Vulcan Aerial Markers](https://www.vulcaninc.com/?p=vulcan_utility_signs_aerial_markers)** > > Vulcan Utility Signs - Products - Vulcan Aerial Markers. ---
**Author:** ![bizerta](https://avatars.discourse-cdn.com/v4/letter/b/3be4f8/32.png) [@bizerta](https://boards.straightdope.com/u/bizerta)\ **Post date:** [May 8, 2014, 9:36pm UTC](https://boards.straightdope.com/t/yellow-signs-with-three-digits-what-are-they/688005/5 "2014-05-08T21:36:33Z")
> [@That\_Don\_Guy](#): > > I have seen a few poles that have two identical signs, facing opposite directions and at an angle (as if they were meant to be seen from altitude). Each sign has three digits, with the third as a superscript as if the number was meant to be from 0.0 to 99.9. > > One sign is pretty much at the end of an airport runway, and another is about 10 miles north and could be aligned so that a plane going to/from that same runway could see it, so it’s possible that it has something to do with that, although I can’t find any reference to runway distance/direction signs that look like that anywhere. Like this? [File:Underground gas pipeline sign Oregon.JPG - Wikimedia Commons](http://commons.wikimedia.org/wiki/File:Underground_gas_pipeline_sign_Oregon.JPG) Gas pipes are usually inspected from an altitude of two hundred feet, so the sign is easily visible. ---
**Author:** ![That\_Don\_Guy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/that_don_guy/32/538_2.png) [@That\_Don\_Guy](https://boards.straightdope.com/u/That_Don_Guy)\ **Post date:** [May 8, 2014, 9:51pm UTC](https://boards.straightdope.com/t/yellow-signs-with-three-digits-what-are-they/688005/6 "2014-05-08T21:51:03Z")
> [@bizerta](#): > > Like this? [File:Underground gas pipeline sign Oregon.JPG - Wikimedia Commons](http://commons.wikimedia.org/wiki/File:Underground_gas_pipeline_sign_Oregon.JPG) Gas pipes are usually inspected from an altitude of two hundred feet, so the sign is easily visible. Exactly like that. Thanks. There has been some commotion in part of the San Francisco area when the local utilities company pretty much demanded that everybody should leave the ground above a pipeline clear of trees (I assume the company would cut them down at its own expense) to make aerial inspection and actual access to the pipelines easier. ---
**Author:** ![GusNSpot](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/gusnspot/32/436_2.png) [@GusNSpot](https://boards.straightdope.com/u/GusNSpot)\ **Post date:** [May 9, 2014, 4:20am UTC](https://boards.straightdope.com/t/yellow-signs-with-three-digits-what-are-they/688005/7 "2014-05-09T04:20:57Z")
I have had people try to build their house over a 16" high pressure natural gas line. Not a very good idea and manys peoples goes out to read to them from the book. Also we would get fired if we got caught that high ( 200’ ) while on patrol. You can get a nose bleed way up there. Can’t see much from that far away. Oil field gathering systems were usually done, clear of the trees and/or up to 50’ above ground. OKAY, that was puffed up a bit, add 20’ to the altitudes I first said. Turkey farmers will shoot at you if you’re not at least a 500’ away. A lot of companies have painted fence posts at the edges of the roads. Color coded so they can be positively identified. ---
**Author:** ![Polar\_Iceman](https://avatars.discourse-cdn.com/v4/letter/p/f9ae1b/32.png) [@Polar\_Iceman](https://boards.straightdope.com/u/Polar_Iceman)\ **Post date:** [May 9, 2014, 4:40am UTC](https://boards.straightdope.com/t/yellow-signs-with-three-digits-what-are-they/688005/8 "2014-05-09T04:40:46Z")
> [@bizerta](#): > > Like this? [File:Underground gas pipeline sign Oregon.JPG - Wikimedia Commons](http://commons.wikimedia.org/wiki/File:Underground_gas_pipeline_sign_Oregon.JPG) Gas pipes are usually inspected from an altitude of two hundred feet, so the sign is easily visible. How exactly do you inspect a buried pipeline from 200ft? And what exactly would you expect to see? Color me confused. ---
**Author:** ![GusNSpot](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/gusnspot/32/436_2.png) [@GusNSpot](https://boards.straightdope.com/u/GusNSpot)\ **Post date:** [May 9, 2014, 4:46pm UTC](https://boards.straightdope.com/t/yellow-signs-with-three-digits-what-are-they/688005/9 "2014-05-09T16:46:57Z")
Physical intrusion. Amazing how may fol;ks there are who will run their ditch digger without checking things. Leaks usually cause discoloring in the vegetation. Dust coming from a single point is also a clue. Survey or land clearing for a dwelling. Vandalism. Loops & valves seem to get rifle rounds fired into them. Holes ya know… Why we were lower than 200’. A reference for the pilots to use in reporting. In flight flight planning for various reasons.