Spark

From TibiaWiki

A yellow spark is shown on the monster/player that you've attacked when the armor absorbs the damage done from a hit. Hits that cause a spark do not count towards your shielding skill.

When a monster is immune to certain damage types (physical or magical), it also produces sparks.

Sparks show also during skinning with Obsidian Knife. Green spark means successful skinning and yellow one on unsuccessful try.

When a player uses a furniture kit outside of their house, it will also produce sparks. The sparks appear where the kit is, so when it's in a backpack, the sparks appear on the player's character as if it's being hit.