IF it was ''sized' ( a special undercoating) it will come off the wall readily,,if not all bets are off.Is there an inconspicuous spot to see how it was installed. 

Apply amyl acetate if available or nail polish remover -PRETEST INCONSPICUOUS AREA FIRST. 3.

Bandit signs on telephone poles however, will get you a lower response rate due to the fact that they're a bit inconspicuous, but I've had some stay posted for 4+ months and generate a slow trickle of phone calls the entire duration.

We were able to leave the deactivated K&T in the walls.K&T aside, if the building is old enough to have lath-n-plaster, I'd pick a inconspicuous spot along an external wall and make a hole to see if there is any insulation, or just another layer of lath-n-plaster in the cavities between studs {a common practice for a wind-barrier}.

I put a lock box (available at Home Depot) on the property in an inconspicuous place.

If you go with conventional door locks, hide one in an inconspicuous area so that when the tenants lock themselves out at 2:15 in the morning you don't have to make a trip to let them in. 

Originally posted by @Mike Hayes:@John Thedford I doubt anyone is worried about you reporting them Actually the "skilled" lawbreakers do tend to operate as inconspicuous as possible.

You might consider an inconspicuously place mounted lockbox somewhere on the property.

My daily driver is an Acura which is a pretty inconspicuous luxury car. 

Can be totally inconspicuous, and then you can get an idea of what's going on inside there.