At the time of writing Glow Squids did not appear naturally in the world and can only be created using creation eggs obtained from the Creative Mode inventory.
The behavior of Glow Squids is almost completely similar to ordinary squids. They will float aimlessly in the water, emitting particles. On land without water, Glow Squids can die.
If someone attacks them, they stop glowing for 100 game ticks (5 seconds) and try to swim away, doing it much faster than ordinary squids.
After death at the hands of a player or a tamed wolf, 1-3 experience drops from the Glow Squids, as well as 1-3 glowing ink bags
Glow Ink Sac
A glowing ink bag is an item that falls out of the Glow Squids after death. It can be used to create new ones in the workbench Glow Item Frame, as well as highlight the text on the plates with them.
Glow Item Frame
Luminous signs are distinguished from ordinary ones by the fact that in the dark they are illuminated and highlight the object that is in them.
Use A glowing ink bag is also possible on the plates to highlight the text! In the screenshot below, you can see the difference between the text on a regular sign and a glowing one.
Such plates are created from Glow Ink Sac and sign.