Sign text color: Can't enter the § symbol
Solution 1:
Formatting codes aren't used to change text colour in Java Edition. They can't be entered into most text fields, and these text colour changes cannot be made without cheats.
If you are trying to change the sign colour in Survival, instead try the dye method. Right-click on a sign while holding a dye to change its text colour.
If you are looking for a multi-coloured sign or don't like the colours the dyes give you, you'll need to use cheats to customize the sign's raw JSON text.