So looks like a -.25em margin is being applied to signature blocks. (forums.penny-arcade.com/applications/dashboard/scss/compatibility/editor/_richEditorLegacy.scss line 68) I didn't dig into exactly how it's calculated, but I'm seeing the same thing on Chrome and Edge. Anyways, text looks alright, but if the first thing in your signature is an image, it is cutting off the top of it unless you add something else to eat the first-child selector. Looks like that file in particular is part of vanilla, but could be fixed with an override?