Comment by Ajedi32

Perhaps that could work in certain situations, but you don't even necessarily need digital signatures for that. A link to a reputable news site claiming they've verified the footage as real would be good enough in like 95% of cases, people just don't bother to check.

You'd also need close to 100% adoption for this to be effective, otherwise people will just assume the fakes were recorded with one of the cameras that doesn't have that feature, or that they didn't bother to upload the raw footage anywhere.