How do they do it? Is it UV or something more destructive?

Waste of time in my opinion. If it’s stolen you’ve still got to rely on them finding it.

UV pens and Smartwater are the two I know about, but there may well be other things

He he he.. We used to have a set of postcode stamps at every front counter, just for this reason. The method was to turn the bike upside down, try and get the stamps in the right order, get out the girt big hammer and find a spot on the bottom bracket and BOOM..!

The look on some poor lads face who’s brought in his pride and joy under orders from his dad.