(a.) Is the hand supposed to help people determine how much five dollars is, in case they can't read numerals and need a visual cue?
If so, they probably can't read dollar signs either. They might think that Subway is bartering their sandwiches for high-fives, or possibly severed hands.
(b.) Or is it there just to provide scale — to show you how long a foot is? If so, I feel like something other than a hand maybe have sufficed, such as...a foot.