I'm not going to say there is no H1 H2 L or whatever but if it's the casting marks they're probably not something to concern yourself with, the letter we're looking for stamped on and dicates the correct piston to use;

'A' Cylinder - 'B' Piston
'B' Cylinder - 'No mark' Piston
'C' Cylinder - 'D' Piston

Check the clearance anyway, not with a verni-eye gauge either and if you're replating send the piston away with the cylinder and say what clearance you want rather than trusting something to chance.
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Please do not PM me technical questions, if you can't find it on the Forum start a thread