Have been corresponding periodically with potential advisor and met in person during a campus visit. This person told me to let them know when I applied and that they would write a "note of support" for my application. Is this common? I assume it's like an additional reference letter, except obviously less detailed and not based on an extended knowledge of an applicant's previous work? I don't think this person is on adcomm this year (given that they'll be on leave), but is a senior scholar who's one of the biggest names in the department. So it's a good sign, right?