The Ctrl+PickBlock on a blank sign still opens the GUI upon placement

Partly confirmed, it does copy the NBT data (as seen in the lore) but it doesn't prevent from opening the edit sign gui.

Changing report accordingly.

Can confirm for MC 1.12.1.

Confirmed for 1.13.1, but this is most likely intended. 

The sign is empty so if you copy it, and place it would be WAI to actually open the edit gui, so you could write on it.

I see. Should this issue be closed?

What is WAI?

Can confirm in 21w11a.

Can confirm in 21w14a.

Can confirm in 1.17.1.

This issue was present in 1.17.1, but no longer occurs in versions above or equal to 21w37a. With that being said, this issue has been fixed in 21w37a.

Confirmed fixed.