Gyalpi!
is an abbreviation for Gal Piece
It refers to the peace pose in which the V sign is turned upside down and pushed slightly downward.
Resized to 72% of original (view original)
Artist's commentary
ﾃﾞﾃﾞﾆｰでｷﾞｬﾙﾋﾟ
ﾃﾞﾃﾞﾆｰでｷﾞｬﾙﾋﾟ