Diplomacy – or lack of it – shows in writing in general, and will be just as obvious in a signature.
Natural diplomacy shows when the writing become increasingly smaller as the word, or line of writing goes on. But only if the writing also continues to be as legible at the end as it is at the start.
Signatures that start with a couple of letters you can read then disintegrate into a mess of squiggles, or just a long line, do not show diplomacy.
Another indication of diplomacy is the upper case M or N which gets smaller as it goes towards the right.
The absense of one trait does not mean the presence of it’s opposite. So the absense of diplomacy does not mean tactless. There is a separate stroke that shows a lack of tact.
A lack of diplomacy, or bluntness, shows where there are no “lead in” strokes, where, when the pen is first put on the page, the writer gets right into the main part of the letter s/he is writing, without a curvy or straight line leading into it.
This is the person who is likely to put their foot in their mouth rather often.
So if the writer of the signature you are examining goes right into their name with no messing about, expect them to do the same with any topic they choose to discuss!
Good communication skills can help you in any area of life.