S.m.K.Lspur (weiss) = Spitzgeschoss Mit Kern Leuchtspur (Weiss)
Translates to: Pointed Bullet with steel core and tracer (white)
Most commonly used in MGs and Aircraft guns.
If the boxes open easily (you may not want to break their seals), you will likely find a black tipped bullet in either a brass or laqured steel case.