Am i need to sign on invitation letter?

[a1toids]

My parents got appointment on june'20th and i sent them all the papers. But i didn't thought of signing the invitation letter addressed to my parents. Am isupposed to do that?. Is it mandatory?. If so, what options i do have now?

[anna char]

sign the letter, scan it , make a pdf file and send it as an attachment. That is what I did.