What does it mean when someone’s signature has noticeably small capitals?
It is an indication of modesty. This writer does not seek the limelight. S/he may like to be in the center of things, knowing what is going on (this will show if their signature is in the middle of the page) but they don’t want to be noticed and attract attention.
Of course, there is what is called “false modesty” – someone who really longs for attention but pretends they don’t.
The real person shows in the body of the writing, the signature just shows how the person wants to be seen. So if the body of the writing is more flamboyant, attention seeking, with a modest signature, you will know that the modesty is not real and that this writer has, for some reason, decided to look as though they want to be low key, when in reality they seek recognition and attention.