I’ve never seen such a sticker. It sits on the top of the box. What’s the reason for its existence?
Just a guess: maybe the loading is too weak to cycle the action for MG`s.
Not necessarily “too weak” but more in the line of
“Does not meet ballistic specs for MG use” which covers a range of problems.
Also ammo could be downgraded because of “repack”
( mixed lots of unknown lots) or simply age.
Such relabeled ammo was in most cases relegated to secondary or training use. Ammo for the fighting fronts was usually the latest made universal use ammo.
Normally cartridges without an additional marking on the label were for use in machineguns
Some companies stamped the label with „iL“ „in Ladestreifen“ or Für Gewehr for cartridges loaded in clips.
Hirtenberg did this by this additional label on the box.
It was not usefully for using cartridges shipped with clips if they were loaded in belts for a MG.