Yes pleasseeeeeeeee. I don't know how much it would cost, but I would gladly pitch in if I had to. I have near misses with people riding way too fast through there all the time (and still have some near misses with people going super-slow since it's so narrow and so blind).
If we can't have legitimate trail infrastructure there, we should at least get something like that. It's ridiculous that's supposed to be part of a bike trail but that they made it so narrow that they have to put up signs telling you not to ride your bike through it