I do not have information covering Austrian World War I unit stamps. I can only guess.
The R may signify Regiment.
MC ???. If MG I would guess machine gun.
Sorry that I cannot be of more help.
Below is a little more detailed guess. Unit markings instructions for Imperial Austro-Hungarian units have not surfaced and it is difficult to be certain about the unit designations.
Roth Steyr, Steyr mfg., sn 7059, 4 R M C (G?) 12 : 4 Infantry Regiment, Machinengewehr-Kompagnie, waffen no. 12)
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