I’m not sure if this is an intended Bedrock Edition feature but signs aren’t a full block long in width so when you put multiple next to each other you can see a little gap. This is shown in the pictures below.

Steps to Reproduce:
1. Place down two signs of any type next to each other (either on the wall or on the ground, it doesn’t matter).

Observed Results:
The shorter side of the signs don’t touch as they aren’t full blocks.

Expected Results:
In Java Edition the shorter side of the signs are full blocks, meaning signs touch when placed next to each other.