If a particular address was known to consistently receive cash in the mail, wouldn't that make it a target of theft?

As someone who lives in the Bay Area and has seen car windows smashed for the change in the cupholder and a friend's motorcycle knocked over to get the flattened soda can that was being used as a stabilizer, yes, that's a security concern.

Just socks, maybe the $10 bills were stolen ;-)

A transient mailing of discrete paper cash is different than a call-to-action requesting coins that will be delivered to the same address on a regular basis.