The Bug:

minecraft.used:minecraft.ink_sac doesn't increase when applying an ink sac to a sign.

Steps to Reproduce:

• Create a scoreboard objective for tracking the use of an ink sac and set it to display on the sidebar.

/scoreboard objectives add UseInkSac minecraft.used:minecraft.ink_sac
/scoreboard objectives setdisplay sidebar UseInkSac

• Right-click on a sign whilst holding an ink sac.
  →  Notice how the scoreboard doesn't increase.