Instructions on MG151/20 gun cover
 

Hi everyone,

I'm wondering what was the typical - if not standard - notices or plates on MG151/20 cover within Bf109 G cockpits (both above WNr., please see attached pic).

http://www.clubhyper.com/reference/l...29_cockpit.jpg

Could anyone especially tell if there was a standard pattern for these markings on MG151/20 covers (Waffenabdeckung), or just depending on factory ?
I suspect they might be related to engines warm-up procedures, or at least linked to engine rather than MG151 itself...