I think 홍낙찌 here might be a nickname for the intended recipient of the note. The word seems to be made of 홍(family name) plus 낙지 (small octopus). That fish(mollusks) probably reflects a physical characteristic of the recipient in a sense. This is my own thought, and some people could speculate differently.Hongnakji (name?)
In response to my question, 국어국립원(the government-run body that defines the Korean language) answers that it is difficult for them to confirm if the use of ~있제 is a dialect because there is no relevant information in their dictionary database.Question for people who know: is the 제 verb ending a dialect of 지?