Coming back to the old stuff...

@item -O
Select a more optimal output mode for your terminal rather than true VT100
emulation (only affects auto-margin  terminals  without @samp{LP}). This
can also be set in your @file{.screenrc} by specifying @samp{OP} in the
@code{termcap} command.

...and also in the man page (like it should be).

-O   selects an optimal output mode for your terminal rather than true
VT100 emulation (only affects auto-margin terminals without `LP').
This can also be set in your .screenrc by specifying `OP' in a
termcap command.

Let's (finally) close it.

Should probably check to see what other options may not appear in the documentation (or --help output).