According to a quick Google search, a Shriner clown appears to be a clown who is also a member of the Shriners.
Sister Shriner is boiling over with railing toward God's pure little ones.
Later it developed the janitor was a captain of police, also a Shriner.
Mr. Shriner, the one of whom we expected least, suddenly turned up at a table alone.
1882, a member of the Order of Nobles of the Mystic Shrine (established 1872).