I
think it was originally for making it easy open, since the closer to the tip the nick is, the more leverage to open.
NOTE: I am
probably mistaken.
I've seen them on the Rough Ryder 2 blade Folding Hunter.
To me they are ugly and a deal murderer. Maybe if they didn't have the match strike pulls they would look better. Personally, I "wish" they would drop the tang end nick for looks.
All my RR except the stockman's, have a "5" pull. The stockman's are all a Buck 301-ish "4", whether a 3.75" closed Sowbelly, to a "XL" 4.25" closed model.
Taking that into consideration, the tang end nicks would
probably be enough that it would not be necessary to fight with the knife to open it.
I have seen a few vintage single blade slipjoint folding hunters with twin nicks. "The Why" is beyond my pay grade;
EVERY single blade slipjoint folding hunter I've seen was equipped with a pinchable blade ... even moreso than a Buck 110 and a Old Timer 6OT/7OT's blade.