Natasha's soul mark is unique.
She is born with it.
The mark is that of a beautiful bow an arrow.
Its blue-gray in color.
Clint's soul mark appears when he is five.
It is of a spider weaving a web.
The spider is black.
But its the web that catches his attention, it is red in color
Years later, when Black Widow and Hawkeye meet, they feel a tug in there hearts.
The know they are destined.