All Hail The Rat

The egg with hatchet and pistol is probably the most iconic of the Mercenary army's unit insignias. It was originally released as one of the decal options for the Nitto S.A.F.S. and has recently been re-released by Hasegawa on the new decal sheet included with their 'Ma.K figure set A (Mercenary Troops' Arms Cold District Maintenance Soldiers)'. According to notes on the cards that came with the figure set, the markings belong to the 15th AT regiment.

I believe that the 'egg' symbol is a pastiche of the emblems of two Luftwaffe Aces, Adolf "Dolfo" Joseph Ferdinand Galland and Lieutenant Colonel Oskar-Heinz (Heinrich) "Pritzl" Bär. Both men (who were apparently good friends) had variations of 'Micky Maus' painted on their planes and the 'egg' seems to borrow elements from both. Clearly the hatchet, pistol and pose come from Galland's ...

"Adolf was a constant cigar smoker. In fact the insignia on his Messerschmitt depicted a cigar smoking Mickey Maus also brandishing a pistol and hatchet! It was said that Galland got through 20 cigars a day and actually wrote orders giving him permission to smoke while flying on a mission. His was the only Messerscmitt with a cigar lighter and a cigar holder for when he was on oxygen."

... while the red circle was likely inspired by the blue one around Heinrich's Maus (which was also the unit symbol of 1./JG 51)

The origin of both 'Mickys' goes back as far as the Spanish Civil War (of which Galland was a veteran), as can be seen in this picture of Condor Legion pilot Hans Schhmoller-Haldy ...

"The 8th Staffel’s Oblt. Edu Neumann, inspired by the popularity of Mickey Mouse among the Condor Legion veterans, adopted another cartoon character as a symbol for his then 4th Staffel and took it with him to the 8th. He made it known that his choice, Adamson, was a good German rather than an American."

It appears that 'Steamboat Willie' had enjoyed a long history with the Luft even before the war ...

Above is another example of a Condor Legion 'Micky'.

Luftwaffe Ace Horst Carganico also famously displayed a 'Micky Maus' on his Bf. 109G-6 ... another of many examples of the nefarious rodent's ever changing allegiances during the war.

Mickey Mouse ... a true mercenary!