Not so much hidden significance, more blatant tbh.
It's just a poignant sign that they must get along well off the pitch and have quite a close friendship if they're all coming up with little things like that. It suggests more of a bond between the core group (like they have a little club, rather than just being at one).
Unless Poch has thrown in secret handshake drills into training, it's signifying a positive nucleus to the team relationships.
I just think Dele is a bit of a wind up merchant as well - he'll love that a handshake is pissing off opposition fans.