So, I’ve been thinking.
When you stop at a cafe and have to leave the bike outside, there’s always the risk of it being ridden off by some unscrupulous ner-do well. SO to combat this you could lock it up, but a lock that’ll withstand more than a pair of cutters to get through it can be a bit cumbersome, and carrying anything bigger on a road bike is a right PITA.
So, how’s about using a small padlock (that would easily fit in your jersey pocket) fitted and locked through one of the jockey wheels and mech cage? It would stop the bike being ridden off, and a bike being carried by a plain clothed yobber looks rather odd, don’t you agree?