Do I sign a 2018 return in black or blue ink?

[DoninGA]

Either, black or blue.

[xmasbaby0]

Either one is fine---just use ink. and sign it and date it.  If it is a joint return both spouses must sign.

When you mail a tax return, you need to attach any documents showing tax withheld, such as your W-2’s or any 1099’s.  Use a mailing service that will track it, such as UPS or certified mail so you will know the IRS/state received the return.