Some people use the serrated area for the index finger of the support hand. I do not teach that hold, but watch the people at the range and see how many use it.
"A well regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed."
Life Member NRA
Life Member NAHC
Former President of the ECPT (Eifel Combat Pistol Team)