In Prince of Persia: The Lost Crown, you can use Memory Shards to mark specific locations on the world map with a Memory.
Memory Shards are unlocked early in the game once you reach your first Wak Wak Tree, and before you reach The Haven, the game's central hub.

To place a Memory, tap the memory shard icon on the top-left area of your HUD (right below the HP bar) or press the assigned key on your controller. 
You can also tap/press and hold the shard icon or the assigned key (for controller) to place a Memory   and immediately open the world map.
 

If you run out of Memory Shards, you can delete a placed Memory.
 
To delete a Memory: 
•  Open the world map.
•  Choose a Memory and select "View".
•  Select "Delete"  and confirm with "Remove".
You can find additional Memory Shards in chests by exploring Mount Qaf.