..All your plant and trailers will have a serial number of sorts on it. You can contact your local police station and ask them to put your gear on the Police National Computer. If they are stolen and a copper subsequently does a thorough check of Mr Dodgy Geezer and his van, if your machines / trailer are there he will be lifted and your machines returned.
You could also get yourself an ultraviolet pen from most stationers and mark each item as follows...
House Number,Followed by postcode.
So if you live at 65 Smith Street OL12 3BT, you should mark your stuff thus...
65OL123BT.
again a quick check with an ultraviolet light ,as they have in shops, will reveal the unique number you have given it.
Hope it all helps..
Locko.