This sign is a variation of the sign "opposite." It is used when describing where things are. For example, the "DMV is across from the Library." (By the way, DMV stands for Department of Motor Vehicles.)
An approach would be to sign "library" 
then use a classifier "A" 
to show the location of the library. then hold the sign "opposite"
near where you signed the "classifier A." Then holding either
the right or left hand stationary, (whichever one is on the side of the
library) move the other hand in a slight arc to the other side of the street.
There are other approaches such as just pointing to a spot in the air with
your dominant hand and then doing the opposite sign -- moving the
non-dominant hand toward the target.
across-from
Sign: across-from
Synonyms:
Handshape:
Right Hand:
Left Hand:
Location:
Orientation:
Movement:
Non-Manual Marker:
Interpretations:
Inflections:
