I seem to have a vague recollection of something like what you’re describing. Unfortunately, it’s been a long time so so the memory is not sharp. I don’t recall ever coming across one when I had my motorcycle, but I don’t believe I ever took it over a bridge.
Any similar sign I would have seen would have been in Michigan, if location matters.
Something sport/touring, like a Triumph Sprint, sounds like what I’d be looking for. That seems like it might be too big for a first bike, though. All the advice seems to be to work up to something that size. Toward that end, I’m not sure what to start with.
I would have either seen it out in the northwest, near Seattle, or here in Boston. In either place, I can only think of a few bridges where a sign like that might be placed.
Someone upthread said these bridges are usually short, but I’m not sure if that’s necessarily true. I think I’ve seen suspension bridges with grated metal road decks. Always figured that was to let the air flow through so it doesn’t oscillate when the wind blows, which can be bad.
There’s a thread about professors who know their subjects cold, but never learn how to really teach what they know. I had a similar experience in this class. I’m sure they’re great riders, and that the techniques they’re looking for are sound. But just saying “turn your head” wasn’t really helping me. Tell me where my visual focus should be; middle of the turn, end of the turn, as far as possible along my direction of travel. If I’m trying to process the right visual information, my head will turn to get it.
One thing I really try to avoid thinking about when I’m going over a metal bridge- falling. Sliding along that bridge would be just like sliding over a huge cheesegrater. I always wear all my gear, and I’m not sure that would help at all. I don’t understand riders who go out in shorts and short sleeve shirts.
I am so misunderstood… 
Yeah, it’s all breezy & comfy 'til you lose some skin.
I get geared up on one of these. The other, not so much. It’s not that I drop the red one, but I can’t drop the black one!
NHTSA does have an e-mail address. I sent them my question and got a reply today. I suspect it’s just a canned response with a link to the Manual on Uniform Traffic Control Devices (MUTCD), a nigh-comprehensive document that could keep even the most jaded road sign enthusiast entertained for days. I haven’t finished researching the issue yet, but I suspect it may not be much help. As I recall, the signs were black text on white, and would thus predate the black-pictograms-on-yellow era of traffic signage.
The reply came from Michael Jordan at dot.gov. It’s so nice that he’s found a way to keep himself occupied since leaving basketball.
There’s a bridge in Philadelphia, PA, USA that has a particularly long stretch of metal grating as both sides of the bride draw open. For years there was a sign that showed a motorcycle rider graphic and some message about weaving or such.
What a wonderful wedding night image!
I’m sure I’ve seen such a sign on the old Jamestown bridge, which was a long, undivided steel grate bridge and was scary as hell to drive over even in a car if there was any wind whatsoever. Unfortunately they blew it up a few years ago, so there’s no way to check.
I didn’t find a sign like the one you describe, but here’s a page claiming that you’re not supposed to swerve on a grated surface. Scroll about three-quarters down the page. Here’s the accompanying image.
