I hope this didnt come up to often but I had this inconvinience right now again. I have quite "big" field for the early game status I am in currently. And especially as an not that familiar player I dont know which seed look like what, so I accidently mixed up my seeds as I bought not enough on the first day. If I had signs where I can say: "This is a melon farm, This is hot pepper, etc" This problem would be solved for me at least. Also if you want to make a bigger storage room for your chests signs would be a nice way to orient yourself. These are the reasons why I think signs wouldnt hurt the game. One could structure his/her farm better and wouldnt be in the sitatuation where one mixed up seeds.
