A Greek cross rotated by 
, also called the crux decussata, illustrated schematically
above in polyomino form. The multiplication sign 
is based on Saint Andrew's cross
(Bergamini 1969).
Saint Andrew's Cross
See also
Cross, Greek Cross, Multiplication SignExplore with Wolfram|Alpha
References
Bergamini, D. Mathematics. New York: Time-Life Books, p. 11, 1969.Referenced on Wolfram|Alpha
Saint Andrew's CrossCite this as:
Weisstein, Eric W. "Saint Andrew's Cross." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/SaintAndrewsCross.html