OP- Being the bike was in the bushes of the neighbors yard or property, you really have no business on taking it... regardless. Could be a gold plated Colnago or rusty heap Huffy, the possibility of being charged with theft is unlikely but would never rule it out.
Now if its at the curb and or easement during garbage pickup day, you have a good case of claiming. Same as when the vultures circle during evictions governed by a county sheriff. If its at the curb, well then...
Not wanting to think much more of this particular matter, but some like old bikes as lawn ornaments. If these neighbors think this is in good taste, good lord!