Alex.
You could always chuck an FT7800 at them. ( In house joke for those that don’t know.)
Ken.
Or even an ■■■077. 
BFN.
Carry one of those “■■■■ alarms” that women use. They’re perfectly legal and whilst they may not bring every copper in the vicinity rushing out of McDonalds they might just put someone off clobbering you.
I did a bit of dead-drop work a few years ago, delivering to Fenners Belts depots and some of them were on industrial estates in the rougher parts of East Midlands towns. Never had any hassle but you did see quite a few serriously dodgy characters about.