Most gnu-screen questions are computer user questions, not computer programming questions, so they are off-topic on Stack Overflow and on-topic on Super User and Unix & Linux (or occasionally Ask Ubuntu if the question is absolutely tied to Ubuntu, or Ask Different if the question is specific to Mac OS X, or Server Fault if screen is being used specifically to aid in the management of multiple computers).
Since only Super User is a migration target from Stack Overflow, migrate these questions to Super User unless you have a compelling reason to choose another site. (Server Fault is also a migration target, but most gnu-screen questions are not SF material.)
Remember the golden rule of migrations: migration is “we want it”, not “let them have it”. If you wouldn't be comfortable having the question on “your” site, don't vote or flag for migration. If you're not sure whether the question is on-topic on the potential target site, don't vote for migration (if there's no migration path and you think that the question is good but misplaced, it's ok to flag; moderators will ask moderators of the target site if they're in doubt).
It's ok to vote to close and migrate to Super User as long as you're reasonably confident that the question is on-topic there (if the question is about Screen, it probably is) and you follow the first corollary of the golden rule: don't migrate crud.