It's the Mnemonics banner! A deposit of fossils are visible in a soul sand valley.

Mnemonics is a basic experience storage mod for Fabric*, inspired by Openblocks and Automagy. It adds 3 blocks and 1 item.

*Seems to work great on Sinytra, too. Best-effort support will be given.

Fossils are an experience storage device found as an ore deposit in soul sand. Standing on one will absorb your experience, and breaking it will give experience back, at a loss. It holds 30 levels of experience (or 1395 points).

Aggregators, crafted with a fossil and copper (bricks in 1.16.5), can be interacted with to losslessly extract 1 level of experience from any adjacent fossil. This xp is given to you as orbs, for mending purposes.

Jars are portable craftable experience storage. They can interact with aggregators and fossils, and store 465 points of experience (1/3 of a fossil). They also stack to 16. A double chest of jars can store 401,760 points of experience, if you're curious.

There's also a dedicated experience bottle item if you want that for some reason. It can hold up to 155 points.

Mnemonics was designed with redstone in mind and most things you'd expect to work do. Applicable devices have comparator support, jars can be placed and displaced with dispensers and pistons, and fossils collect xp orbs and bottles 'o enchanting directly. In the wild I've seen people deploy Create's XP nuggets onto fossils to great effect.

Mnemonics seems to work with mods that rebalance the experience curve. All of Mnemonics' devices store xp as a function of points, so if you want to use a linear xp mod, consider tuning the curve so that level 30 is still 1395 points.