Bicycle detail

On the NE corner of Seneca and Boylston, I locked the front wheel and frame of my Trek mountain bike with a very strong black Kryptonite U lock to a street sign around 5pm on 11/3/2020 and the next morning I noticed that my bike and the street sign weren't there. Only a couple bolts and washers were there, making it very likely that someone unbolted the street sign in order to steal my bike. I don't have a serial number for the bike because it was used when I got it about 15 years ago. I had converted the bike to an electric bike which had a 350W motor in the hub of the front wheel, a battery mounted to the inside frame vertical bar and two throttles (one on each handle). I bought the Hill Topper Electric Bike Kit Battery type: 36v 350w 15-40 mile 6-lb Horizon $849 kit (Part number HT-26-Horiz). I installed this kit on my bike, as well as a rack over the back wheel.