Recently I was looking for a list of available icons for the buttons on the form because the standard forms have a rather beautiful design and many symbol font.
As it turned out, there are a lot of icons available from the out-of-box, and their list is updated from version to version. You can view all
on this link.
You can use these icons by specifying their name in the
Normal Image property on the button control on the form:
Article on the official documentation site