Signs don't hop to the next line after filling out a line like the typing cursor would normally do when typing. I've noticed this for a while now and haven't reported it yet.
Comments 2
Thank you for your report!
However, this issue is Invalid.
You have posted a feature request or a suggestion. This site is for bug reports only.
For suggestions, please visit Minecraft Suggestions on Reddit or visit the Feedback website.
Quick Links:
📓 Bug Tracker Guidelines – 💬 Community Support – 📧 Mojang Support
📓 Project Summary – ✍️ Feedback and Suggestions – 📖 Game Wiki
Have you tried pressing enter, it did that to me, and enter worked, it might have been updates that have changed it from it going automatically to enter.