i do it because i want people to understand me and not abuse me because im slow at processing language,think and communicate differently and have severe trouble interacting one on one.
ive had A LOT of trouble getting understood on forums,and have had A LOT of abuse,by explaining in my signitature i have severe autism and mild intelectual disability it helps lower the level of abuse towards me and it can increase understanding and support when im not understanding something.

it makes sense to put your diagnoses and meds in your signature,people might be able to dcompare themselves and get help from you;they may just want a friend they can compare with.i wont put my meds in my signature as im on to many.