"in rom."
If the title proper of the work being cited in the 670 is in
a language which uses the roman alphabet, then citations from it elsewhere
in the 670 are assumed also to be in the roman alphabet--
so "in rom." is not needed for them.
But if they are citations from another alphabet found
in the work, that alphabet needs
to be identified-- so "in Cyr.,"
"in Heb.", "in Ara." and so on are used where we
normally encounter "in rom."