Personal or friendly email should only have personal details but no official details except email ID (if required).
Similar to Business signatures, personal email signatures should be left indent and with same color as email text. But it can be any number of lines, even one liner email signatures are OK.
Samples of Personal Email Signature.
firstname.lastname@example.org | 098-765-4321
email@example.com | 098-765-4321
Note and Conclusion:
As personal emails are sent only to friends or family, hence there is no need to follow any email etiquette. But keeping a signature will definitely be helpful understand who has sent email.
Adding email signature can also help in searching email when receiver search by your name.