I'm a lot more familiar with ASTM and SAE markings simply because I come from a generation where machinery and Automobiles were still built in this country using American steel and American Fasteners made to American Standards.

ASTM and SAE bolts have markings on their heads that denote their grade.

The three most common that I've encountered are Hex Head bolts Grades 2,5 and 8....soft to hard in that order.

Grade #2 Bolts are soft (relatively speaking) have a smooth head surface without any markings.
Grade #5 Bolts have medium hardness and 3 slashes on the (flat) circumference of the bolt head spaced at 120 degrees apart.
Grade #8 (hardened bolts) have 6 slashes on the (flat)circumference of the bolt head spaced at 60 degrees apart.

There are numerous other bolt grades.
There are also Metric Grades of bolts that we deal with daily in this country.

This web site gives a lot of information about bolt grades and identification markings.
http://www.portlandbolt.com/technicalinformation/fastener_identification_markings.html

hope this helps
steve