Around 1978 there was a National Lampoon’s True Facts photo which showed a shed sporting a nicely-made sign which designated as a place for:
I wish I had a dime for every time I’ve thought about that sign since then. It was ace.
When I was a kid, the local railway station had two ticket windows, one of which was usually very obviously closed. It had a sign on it saying: “THIS WINDOW IS CLOSED”. I’ve always liked that.
And a cool piece of graffiti on the back of a toilet cubicle door: “PROPOSED SITE FOR COAT HOOK”. 
Seriously, the sign in the OP might be something like the ones we have on highways in cold parts of Australia, saying “SNOW AND ICE SIGN”, which the first time you see it seems as silly as a stop sign which says “STOP SIGN” on it. It’s even more odd if you see your first one in the blistering heat of high summer at noon. In actual fact, the sign has a little, difficult-to-see flap on it which is folded down in snow conditions to say “ROAD BLOCKED BY SNOW/ICE AT…” I guess it doesn’t make an awful lot of sense to dig the sign posts out of the concrete each spring.
Still not as good as a sign saying
QUICK!
HIDE!
Ah. Whom am I kidding.
I don’t have any jokes to make about self-contradicory things, unless you people think Lorentz transforms are inherently funny.
I just wanted to wave “hello” to Francesca, because I haven’t seen her around lately. I probably just wasn’t looking in the right places. She’s cute, you know. And English, which gets her extra cute points. Besides, she’s tiny. You could put her in your pocket and take her home. She’s just that little.
Okay, In the spirit of the thread, I’ll give you a punch-line. I’m not doing the whole joke, because that would require a lot of <symbol> coding, and you guys don’t care anyway. I’m not coding the punch line either, not that it needs it. Here it is:
“No, you idiot, you still have to integrate that.”
Bwahaaahaaahaaa!
Erm… sorry.
Man, I really miss posting in the Rue thread, don’t I?
Getting back to the OP, I drive through Queens every day, and every day, I drive past a sign that says, “Now Leaving Traffic Safety Zone.”
So I immediately gun it.
Hell, deregulation is good for everybody, yes?
I passed by this sign yesterday. I had to take a picture.
Wow, and I thought I was the only one who took photos of palindromic numbers! I’m not alone! 
I’d like to see a “Beware of Signs” sign in an area with a lot of uneccessary signs in it.
The other week I passed a sign that I thought said “Wildfires in Progress”, something I knew was happening in other parts of the country but not (at the time) in NJ, so I was rather puzzled why the state highway department needed to tell me that parts of the country nowhere near me were in flames.
Then I realized that what it actually said was “Wildflowers in Progress”, which I found to be equally puzzling. Where are the wildflowers progressing to? Are we supposed to stop and let them pass, or is this more of an evolutionary thing and they’re starting to create their own little wildflower civilization?
Eventually some friends told me that the sign meant that the state had recently planted wildflowers in the area near the sign.
I’m still not sure why they needed to inform motorists of this fact, or why they chose such a roundabout way of doing so, but at least I don’t have to worry about coming to a screaching halt to let mobile wildflowers cross the interstate highway. I’ve had enough trouble with the NJ fauna doing that lately, I really didn’t need to have to watch out for the flora, too!
There was a sign on Manly golf course for years that said “Please do not lean on this sign”.
You don’t know how badly I want that sign.
Car & Driver printed a sign taken someplace in Ohio that said, "Birthplace of John “Johnny ‘Wad’ Holmes.” Yep, the porn star. The sign was in front of a trailer park, BTW.
You shave your face
After you snooze
And wish you’d had
[This sign not in use]
Burma-Shave
Yeah, I do. 
[sub]Sorry for the inside-joke-ish-ness of this post. To clarify: Mudshark and I have a joint collection of absurd signs. This would be one of our focal pieces lustful sigh. If only[/sub].
There used to be a parking sign near Commercial & 7th ave in Vancouver that said:
§
7:00am -
6:00pm**
EXCEPT
WITH
PERMIT**
I used to like to imagine hapless permit-holders being towed away.
I have actually been away for a while on family business. Thank you for noticing!
Mudshark - mystifyingly, there were actually several of these signs along the stretch of M4 that we drove down. I’m sure no one would notice if you were to pop over to England and nab one.
If I could, I would. I wonder how I would explain that to customs.
Just don’t mention the “q” word.
-this screenname Already in Use.
Can you take a photo of that sign Francesca, I’d really like to see it 