Text on signs will unrender when the players rotation goes over a certain threshold. but if the player is not standing right in front of the sign but instead somewhat to the side, the sign is still visible, but the text is not.

The sweet spot for east facing signs seems to be -9.5 (still visible), -9.6 (half visible), -9.7 (not visible), or -170.4 / -170.3 / -170.2 respectively.

How to reproduce: Place a sign (both standing and wall work) with some text on it, look at the sign from a sharp angle, see the text disappear.