Maybe someone in the law enforcement field can answer this. A couple years ago, I “recovered” several yards of the bright yellow tape the police use to cordon off crime scenes; the tape was carelessly discarded in a public trash can. I’ve used the tape on a couple of occasions (a practical joke on some friends, and as a Halloween decoration) inside buildings on private property. As far as the police are concerned, is this a big “no-no”? 
If so, I would think they should dispose of it with more care.
The answer will of course depend on your jurisdiction, but commonly the answer is yes (with some factors). It is is illegal to use it with the intent to cause people to think that an area has been officially cordoned off by police. Clearly, in your case, when used as a decoration with no intent to defraud you have no problem. However, with regards to your practical jokes you could be in trouble since I assume your practical jokes revolve around the notion of them accepting the police tape as being real.
… have a great sense of humor, right? 
Quasi
I can’t imagine law enforcement caring if you use some crime scene tape, so long as it wasn’t stolen (which this obviously wasn’t) and as long as the use didn’t create some type of public nuisance, traffic hazard, etc.
I’ve even given a few yards of crime scene tape to a friend just for the purpose of a joke.
As always, the safest thing would be to call the local cop shop and ask someone.