Why don't they put that info on blades? You, know one of those "good better and best" charts on the back of tha package. I'll bet very few contractors know that. My own chop saw logic always told me not to use a rip blade, so I just used blades with lots of teeth and labeled for fine cutting.
About that stamp in the blade, HM 12.
My brother told me years ago, the saw sharpening shop he went to used to stamp his blades with his account number. Could that be what the marking is, or do you think its a blade use and tooth angle> Looking again with the tools I have, it looks to be 10 to 12 degrees if I'm measuring correctly.