Cleanliness
This page is a In Kingdom Come: Deliverance, equipment can get dirty and melee weapons can become bloody.
Anytime you travel through puddles, streams, forests, or any other muddy places the filth on your equipment will build up, until an icon appears on it in the inventory screen resembling a black splat. This means your equipment is dirty, and you will be treated as such, negatively affecting how people see you as well as prices when trading.
To remove the mud & grime, you can bathe yourself at a bath house for a fee, or simply wash yourself in a water trough for free.
After hitting someone with your weapon, it will become bloody. This will make you more intimidating, but will affect your reputation in other ways as well, and can even lead to you being accused of murder if you wear a bloody weapon near the scene of a trail side murder.
To remove the blood from your weapon, follow any step you normally would to maintain it: Sharpen it at a grindstone, pay for it's repair, or repair it with a blacksmith's kit.
Dirt and blood on equipment does not impact their performance, but can activate certain perks, such as the "Manly Odour" Perk, which grants 50% bonus Charisma when talking to women while dirty, but at the expense of being 30% less stealthy while dirty.