How to assign name for a screen?

To start a new session

screen -S your_session_name

To rename an existing session

Ctrl+a, : sessionname YOUR_SESSION_NAME Enter

You must be inside the session

To create a new screen with the name foo, use

screen -S foo

Then to reattach it, run

screen -r foo  # or use -x, as in
screen -x foo  # for "Multi display mode" (see the man page)

As already stated, screen -S SESSIONTITLE works for starting a session with a title (SESSIONTITLE), but if you start a session and later decide to change its title. This can be accomplished by using the default key bindings:

Ctrl+a, A

Which prompts:

Set windows title to:SESSIONTITLE

Change SESSIONTITLE by backspacing and typing in the desired title. To confirm the name change and list all titles.

Ctrl+a, "