What does jigsaw puzzle piece icon mean re: mods?

[Cougarific]

At the bottom of the Main Menu page some of my mods have actual icons but some show a jigsaw puzzle piece.

Is that indicating that there's a problem with the mod or just that it does not have a custom icon?

[Pèpè Silvia]

It's just the default icon if the mod doesn't have it's own. It should be fine as long as you don't get errors