I see them mentioned in signatures but I don't know what they are.

Read this Scratch Wiki page, it will explain everything:
https://en.scratch-wiki.info/wiki/Evil_Kumquat

CoolLock wrote:

Read this Scratch Wiki page, it will explain everything:
https://en.scratch-wiki.info/wiki/Evil_Kumquat

Or if it's blocked. (99% it's blocked)

Wiki wrote:

The trend was started in the Scratch 2.0 Beta by the Scratch Team member cheddargirl, who discovered that the image host that held her signature, Imgur, was no longer supported. Instead of rebuilding her old signature, she changed her signature to the following:
"Sadly, my signature was eaten by an evil kumquat.”
The trend spread very quickly, and many signatures now mention kumquats, specifically evil kumquats.

Scratch Website

This trend has also moved out of the forums to the Scratch Website, mostly in studios. Some Scratchers have created accounts called “EvilKumquat” or something similar. The accounts may also say “I ate cheddargirl's siggy” or something similar. Some even post on the forums with their accounts or ‘communicate’ with other kumquat accounts.

Outside of the forums, kumquats are small, oval or round, citrus fruits native to China, unique for being eaten whole with their sweet skin and tart flesh. The post above me explains how it's relevant to Scratch.

tbh kumquats eat siggys, so add some siggy guards like pumpkin and caramel