Unless you mean how do you detect utility poles, in which case visually should suffice ;)
But seriously, it'd be cool if someone could share a photo of one.
I can't imagine that putting stickers on utility poles is illegal ;)
But might be for something like this
http://www.dailytech.com/Federal+Court+Cops+Cant+Spy+on+Your...
https://sipseystreetirregulars.blogspot.com/2011/04/smile-yo...
And the Covert-Systems.com one is clever, but would take dangerous work to install properly. But then, it could maybe communicate via power grid.