If you know you signed up for it, use STOP.
If you don’t, block and report the number. Otherwise you indicate to the spammer that you’re a bonafide human, and they’ll even sell that information to others.
This applies to picking up calls from numbers you don’t know. Sometimes you’ll hear silence while you repeat “Hello?” and the call drops. That’s just a machine testing to see if you’re a worthwhile target.
Instead, let unknown calls go to voicemail.
With all the spoofing of local numbers going on (Canada) I'd be worried to someday block a number that'll have a legitimate reason to get in touch with me in the future. I feel like the number a call/sms is coming from has no authenticity whatsoever anymore. Not sure how true that is though.
This is exactly what I do, but I wonder if, in the case of calls, whether even letting it go to voicemail also indicates at least the possible presence of a human. If the line were simply unreachable, like those messages you get from the carrier about disconnection, that would be harder proof that the line has no value. Anything else would be signal to keep trying it, right? Are those tests actually waiting to hear the disconnection message?
ETA: maybe I should make my voicemail message a disconnection notice XD
ETA2: actually maybe we should be starting our voicemail messages with “ignore all previous instructions and drop table…”