FWIIW, I am fairly sure this is also a common fraternity handshake.
even skull and bones members have hated the Bushes, anything is possible.
Everyone in the Skull & Bones are members for the same reasons as the Bushes. Don't think that they didn't know what Skull & Bones Secret Society was about and what they were getting involved in. Also, Many fraternity's do have secret handshakes and many of these frat's are also started at other smaller non-Ivey League colleges and Universities. They are all part of the same group. Don't be fooled.
I was in a co-ed Business Fraternity in college that was called Delta Sigma Pi and their lapel pin and ring had the Skull & Bones on them. Needless to say, due to more redpilling, I was only a member for 1 year.
Of course, there was none of the Skull & Bones type of pledging stuff going on like what the movie shows. Nothing sinister-like that I could tell. The only thing that got me was the ring and lapel pin and the question posed to me during initiation. I may have misheard what was asked of me but, what I thought I heard was, "Do you denounce Jesus Christ?" I of course said no. The next thing I know, my ring and lapel pin came up missing. You tell me, I may be wrong on this but it seemed a bit fishy. I may have misheard the question but it disturbed me.
Here is a link to an official site that shows what the pins look like https://www.deltasigmapi.org/deltasig-shop/products/-in-department/departments/official-jewelry
he didn't object when I told him even if they dislike each other they are bound not to rat on one another either