If the petition and G28 are signed it may not be an issue. You can always send in another signed letter
Samuel Ouya Maina, Esq. 415.391.6612 email@example.com Law Offices of S. Ouya Maina, PC 332 Pine Street, Suite 707 San Francisco, CA 94104
If it's just the cover letter indicating the documents that were submitted, probably it doesnt matter that it wasnt signed. If it is a material document then it should be signed.