I wrote a pair of calligraphy as a wedding gift for my sister and brother-in-law.

It depends on how you write it. 1, as long as the content, and then sign. So you need to sign and tell others what the relationship is. 2, there is a promotion, and the roll call is for my sister and brother-in-law. There is no need to write anything about it. 3, nothing is needed, just the content. Others can't find you, the relationship between the writer and the recipient. Just sign it.