The design on the button is not a shield but it is a palette with 4 brushes. I looked up “Antique Palette Button” and came across the exact same button. I’ve included the picture below.
The picture was posted on Pinterest and didn’t tell much about it but I have included the link below as well.
I have never seen a button like that but it doesn’t appear to be too too old. It is most likely a blazer button from the early to mid 20th century. A good find none the less!