I don't know anything about Trusted Signing verification, but I do know from reports on 'mini umbrella company fraud' that if you're a fraudster, there are people in the Philippines who will happily sign their name to western countries' official paperwork in exchange for $2000 or so. Understandably, as that's more than the country's median annual income.

So I can see why offering trusted signing for individuals worldwide would come with certain challenges.