MTR 3.8 Game Markers

Small items (e.g. glass beads) may be used as markers and placed on top of a player’s own library or graveyard as a reminder for in-game effects. These markers may not disguise the number of cards remaining in that zone nor completely obscure any card.

Players using markers to represent in-game components (e.g. permanents) must have a way of clearly representing any in-game status, such as whether a permanent is tapped.

Sleeves or card backs that appear similar to any player’s sleeves or card backs may not be used as markers.

A tournament official may disallow the use of game markers that can cause confusion or that are deemed inappropriate or offensive.