Nos.

Etymology
From +  as a nautralization in English irrespective of any New Latin morphology (analogous to the informal variants, , , , and ).

Usage notes
The form Nos. (as with lbs) has been very widely used in English, regardless of any prescriptions that it ought not to be. However, formal writing usually avoids pluralized symbols for units of measure (for example, in SI style a unit symbol does not inflect, so "5 cm" is considered correct).