It Will Be Run Over Thousands of Times

Er...who are you trying to warn? Should we be worried that airport / airplane personnel aren't aware or alert about where the runways are? Or that untrained (unauthorized?) people have slipped by security and may be milling around on the runways looking for a good spot to picnic?

Still, it's a darn interesting sinage spec that you need. I'll see if I can locate anything.

I don't believe that you will find a already manufactured solution as loose signs can be a flight risk. If you have to put up signs to let people know that they are entering a runway they have no business being there. As I have as an outside contractor done business with companies mainly air freight. Having to go beyond the gates of the air field it was procedure to be escorted on.

Paint the information on to the tarmac.

How about a sign mounted to a spring hinge, with the hinge anchored to the ground? If the sign must be portable, mount the hinge to a weighted base -- perhaps a sand or water filled container.

How is this problem dealt with in various airports now? This should be a mature problem with an already evolved optimal solution.

this popped into my mind as well but the problem is that a jet engine can pick up a 150 pound object quite easily and suck it into the intake. youtube has several examples of this having been videoed. That's the problem I can't get past with this one....

The one possibility would be to have a magnetic base but then you need ferrous metal plugs in the tarmac to attach to. Since it would seem that the purpose of the signs is to be mobile as ground traffic shifts that might not be practical.

OK, I'm stumped...

A two foot high sign of any fashion on a taxiway is foolish, IMO, foldable, retractable, or otherwise.

Jet intakes and exhausts are one problem, but my company's airplanes, mostly Beech 90's, 100's and 200's, have props that would likely be within that envelope. We also have heavily instrumented pods with sensors mounted under the belly that might not fare well with such obstacles.

Specifics on size please. And will be mounted on ground, taxiway, tarmac, where?

One possibility might be center reservation (median) traffic markers. These generally lay over in one direction fairly well; but not so well the other direction.

Will try to post pic later. A local civil engineer should be able to steer you, perhaps paving contractor as well.