Sharpie

From Toadwater Guide

A bird that lives in a birdhouse on a Quaking aspen tree. Once in your inventory (see Birds), you can place the sharpie on the ground (select the sharpie then select a square next to yourself). Doing this will list the names of all players in your current world square. Also the sharpie will fly out of your inventory immediately (and back to its home birdhouse if it has at least one more use).

If the sharpie is not used within 10 minutes, it will fly out of your inventory (and back to its home birdhouse if it has at least one more use).

This is most commonly used to find idle characters in a newly establish base. There are many ways to find them once you know how many are on each world square. The easiest method is to contact your friendly neighborhood viceroy and, for a mere 5mill gold get the coordinates for them; or you can try to set workers to fertilize the entire world square, they won't work where someone is standing.