A blot on the/one's escutcheon American British noun phrase
A stain to disgrace one's honor and reputation
James scored an own goal at the important match, which was like a blot on his escutcheon.
Be careful with your word! Don't be a blot on the escutcheon before the friends' presence.
Jenifer is a famous singer, the love scandal will be a blot on her escutcheon for years.
It was often said by a photographer when he would like small children to look at the camera and smile before he took a photo.
When the photographer said “watch the birdie”, all of us looked at the camera and smiled.