This claim has been circulating on Facebook:
Although marijuana is now legal in Colorado, I don't see any particular attraction to mile markers from this state, as US mile markers are pretty standard--at least along interstate highways (where this photo appears to have been taken).
In any case, is there any truth to the claim that the* 420 mile marker has been a special target of theft? And if so, did the CDOT change the mile marker as claimed in the photo? I haven't done any in-depth investigation, but the low quality of the image makes it seem quite possible that it was doctored...
*The claim suggests that there is a single mile marker 420 in Colorado, which is clearly false, as, even if there is only a single (Interstate) highway long enough to have a mile 420, there would be one marker on each side of the road, one for east-bound traffic, one for west-bound.
(A personal note: I'd rather steal a 419.99 mile marker myself....)