Found this on the Mahle site
"Identification Marks
These markings guarantee Quality MAHLE Pistons (on top of piston):
* Maker's quality sign
* Piston diameter in mm
Measured across the greatest skirt diameter (at the bottom of the skirt, perpendicular to the pin axis). On small pistons, mostly, only the measurement group and the nominal diameter are marked. Further information concerning the diameter as well as the fitting clearance are quoted on the package.
* Standard or oversize dimensions in inches
On pistons for engines with cylinder dimensions in inches: "Std." or for example, ".020" for oversizes, in addition to the greatest piston diameter.
* Fitting clearance in mm
Equivalent to the difference in diameter between the cylinder bore and the piston skirt at a temperature of 20'C (68'F).
* Installation direction
The direction of installation in the form of a crankshaft flywheel symbol or an arrow showing the direction with respect to the control side of the engine. The marking "vorn", "Front" or "Abluft" (exhaust air) or a cast-in notch also indicates the installation direction, which must be considered not only because of an asymmetrical crown shape but also on account of the offsetting of the gudgeon hole for noise reasons.
* Additional markings if necessary, e.g. A = Exhaust, E = Intake, 1 = Cylinder 1, Z 2/3 = Cylinders 2 and 3."
Notice the small marking in the pic looks like the top marking on my pistons
