May relate to MC-195473 and/or MC-170902.

The bug

The sign texture has a texture for the "front" of the sign, which is the base plank type, but lightened slightly as to make it look less "noisy" and improve readability of the text, due to this formerly being the only surface of the sign on which can be written.

This was mentioned by Jappa on this comment in MC-199453: "It's to be more readable for text, the contrast is lowered on the front."

As of 23w12a, functionality was added for writing on the back of signs. However, the back texture of the sign has not been changed to account for this, which seems like an oversight.

How to reproduce

1. Place a standing sign
2. Inspect the front
3. Inspect the back

Expected results

The front texture is slightly "more faded"/"less noisy" than the texture of the plank block used to make it. By extension, this should also apply to the back texture in the latest snapshots.

Actual results

The back of signs remains unchanged, making text slightly more difficult to read there.

Further notes

The Programmer Art resource pack makes this difference much more obvious, as the difference between the front and back is much more significant there than in the current default textures there. Fixing this issue for both the current textures and Programmer Art is unlikely since the latter is not supported to the same extent as current textures, but would be preferable for accessibility.