I understand the sentiment of a small, portable cable for locking in direct view. I'd not advise it, but if one does want to purse this strategy, at least make sure that you have a cable that is not something that can be cut with a Leatherman or other pocket tool that may be commonly carried by a passerby. Avoiding that, at least limits the pool of potential thieves to those carrying tools explicitly with the intention of stealing bicycles (heavier duty cutters).

J.