Maybe get the property owner's permission to put a tag on each possibly abandoned lock listing the date, and that if the tag is still present on the lock at the end of 30 days, it will be considered abandoned and will therefore be removed. If the person does not wish the lock to be removed, please remove the tag, and it will not be considered abandoned. Also, when the tags are placed on the lock (with the owner's permission), inform the local police of the tagging of the locks and the date. You should have the tags printed, and possibly have a unique number for each tag. Loop the tag through the shackle of the lock, and staple the ends together, so customer removal of the tags is not a hassle.
At the end of the 30 days, again get the property owner's permission. If the property owner still is willing to authorize the removal of the locks, let the local police know that persuant to previous police notification on XX date, the locks have been considered abandoned for more than 30 days, and the owner has authorized you to remove the locks. If the local police have no problems, then remove the locks.
The bike racks with the locks that I am thinking of are at a local business, and the racks are heavily used. There must be 30 locks that appear to have been there for months, so they would get in the way of those who wish to use the rack.
Do not remove a lock that is actually securing something.
The benefit to the property owner and/or business is the abandoned locks are removed, leaving space for customers. The owners of the lock have the opportunity for a whole month not to remove the lock, but to simply remove the tag from the lock. The police have confirmed that the abandoned locks can be lawfully removed, and have been informed of the process and time. You will have done due diligence in making sure that you are permitted to lawfully remove the locks, and that the locks are truly abandoned.
Just when you think you've learned it all, that is when you find you haven't learned anything yet.