I recently stumbled on an old mahjong set for $20 and had to but it. All the tiles and dice were there but was missing the wind indicator (also called a "bettor") and the pivot corner piece that can be found in most mahjong sets. The wind indicator is meant to keep track of the players when their "wind" changes direction whenever a deal passes. The pivot corner piece is meant to mark the player who was the original "East" player at the start of the round and is meant to be placed in the corner of the table.
When I used to play mahjong with my family, there would always be a wind indicator and pivot piece, so it felt essential to complete the set I had. The pivot piece is traditionally made of green plastic but the wind indicator pieces can be any color combination as long as the direction symbols are clearly visible.
Someone on thingiverse has already designed a full mahjong set so this can be considered an addition to the set if needed.
P.S. Please excuse the shoddy paint job when filling in the characters. I'm and engineer, not much of a painter.
The only piece needed to complete the wind indicator is a small screw to allow the top piece to rotate comfortably on top of the bottom piece.