Well, you have to have some way to explain where you get all that nuyen you're spending.
A forged job certainly helps. Some fake call centre is probably set up in some third world hellhole (Like Seattle) where SINless people act like your co-workers, or just some Voice Mail Hell to go along with High-End SINs.
As for Licenses, I've never seen GMs handle them the same way. I usually go with a "Concealed Carry Permit" License and an Ares or CAS Fake SIN to explain why I have firearms, hunting licenses are also favourites of mine (Explains hunting rifles and shotguns.).
For anything full-auto that you want to try and get past security or whathaveyou, yeah, you're talking a heavy security Fake SIN job. But, honestly, if you're packing like that you're not likely going to care for people checking your SIN and licenses anyhow.
Also, remember how violent and dark the world of the 2050s-2070s is. Watch Predator 2, look for the subway scene. That's Tuesday in Seattle on the Monorail.