How to disable SerializeField attribute related warnings/proposals from MonoDevelop?

You can disable warnings in C# like this:

 #pragma warning disable 649

You can put them at the top of the file, for example.

Edit: For a global solution, you can add compiler instructions.

1. Add a text file named mcs.rsp (Mono-CSharp [compiler].ReSPonse [file]).

2. Add this to the file: -nowarn:649

The nowarn flag works just as the #pragma, with a comma seperated list of warning numbers to ignore.

Another edit: I'd recommend thinking twice before globally disabling these warnings though. They exist for a reason and it might be detrimental to ignore them in all potential situations rather than disabling them deliberately on a case-by-case basis.

Yet another edit: Instead of disabling that warning, I'd recommend using = default on your fields. Like this:

 [SerializeField]
 private int number = default;

Also, note Unity's compiler has slowly gotten updated to allow Unity to suppress the warning automatically for serialized fields, and in some feature update, this won't be necessary at all anymore.