If a prescriptive easement was given by previous owners, would it be recorded anywhere?
No, a prescriptive easement is similar to adverse possession, only instead of the non-owner user gaining full ownership of property through long-term use, they gain an easement for continued use (I believe they can make it official by filing a quiet-title legal action).
You have two choices if you want to make sure nobody can win a prescriptive easement: (1) clearly giving permission for the use of your land while reserving the right to withdraw your permission in future, or (2) successfully keeping people out. Fencing off the property, posting signs, etc. will do no good if people keep using your property anyway.
Whichever you choose, it may be too late if you don't do it within 10 years of when this public use of your property began.
When you bought this property, did you buy title insurance and was it a "Standard" ALTA title policy (bad) or a "Homeowner's" or "Extended" policy (good)? Did you get a copy of the title report while you were in contract, and is this public use of the property listed in the exclusions?
If and when anyone files in court to have a prescriptive easement recognized, that will be a reason to put in a claim against your title insurance if it's covered; otherwise you'll have to hire a lawyer to fight it. Hopefully nobody will know to do this, or care enough.