A house mark is like a special symbol that people use to show which family or group they belong to. Just like how you may have a special symbol on your shirt or bag that shows which school you go to, a house mark is like that but for your family.
Long ago, when people didn't have last names like we do now, they needed a way to show which family they belonged to. So they came up with house marks! These were usually simple pictures or symbols that were easy to remember.
House marks could be things like animals, like a lion or a bird, or even shapes like a star or a triangle. They could also be colors or patterns.
Having a house mark was important because it helped people know who they could trust and who were their friends. If you saw someone with the same house mark as you, you knew that they were part of your family or group, and you would treat them kindly.
Even today, some families still have house marks that they use on things like flags or crests to show their pride in their family history.