Odd Bolt marking

[FloridaAl]

Took apart an older Howse 5' rotary cutter. The shear bolt is bent but not sheared, making me think the bolt may be a grade or two above what's recommended. What was there has an unusual marking (at least to me) on it.
Can anyone identify this bolt marking?
Thanks.
Florida Al

 

[torch]

Looks like the manufacturer's mark for Highland Bolts and Nuts. No other marks, so Grade 2

 

[FloridaAl]

Thanks much.