If you can't go to the scene, you can ask your familiar fans to sign for you.
No longer, even Weibo or some program groups will release some activities. You can participate in the activities according to the way, but it depends on your own luck to get the idol's signature.
Mic album (my idol) I just asked my friend to sign it for me. I am a student fan, so I don't have the time and opportunity to go by myself.