Were they automatically signed up, by dear Government, or, did they voluntarily complete and submit the form.
Which, by the way, wasn’t even compulsory or followed up on…just required.
I remember seeing TV advertisements about males that reach the age of 18 must register with Selective Service. The ad specifically said "it was the law," and they could face jail time if they failed to register as required. If I remember correctly, the registration cards were available at post offices. That's where my sons got theirs to send in, and they each got a card back from the government.