It appears to have many picture frames with SpongeBob's face in them, which correspond to the number of months SpongeBob has worked. Unlike Squidward, SpongeBob has worked hard for many months to have accumulated these awards.
Since these numbers exceed 12, 24, or even 36, it shows he has worked for many years.
In one of the first scenes, SpongeBob tells Gary that Mr. Krabs will be announcing the new manager of the Krusty Krab 2, and says that he believes that he will be the new manager because he has 374 consecutive employee of the month awards. He shows Gary a wall of his awards that he has in their bedroom.
In certain episodes, where this object appears, the number of picture frames can change, which decides how many years SpongeBob has worked at the Krusty Krab.
Also, in some episodes, the location of the object has changed. For example, in its debuting episode ("Employee of the Month"), in was on the wall of the Krusty Krab where Squidward's post is, but in "Breath of Fresh Squidward," it is shown inside the kitchen where SpongeBob works.