I had the same thing happen on my property 2 years ago. I never posted it but that started me posting. I also found out the probable theif cruises around on a quad and steals others also. So I set out a spike strip at the property line and approx 50 yards further down the trail posted a sign: GOT YOUR FIX A FLAT? He is no longer riding because I noticed the trails are completely covered in now with weeds.