Headcanon: The Marauders’ handwriting
James: changes very often. One day, he circles the top of the i, the next day he dots it, and the next after that he doesn’t put anything above the i at all. Some characteristics of cursive lettering is always present in James’ handwriting, and it always stays in the same generic size, but otherwise, you never know what to expect. It could be super neat and tidy, but just as often it is the exact opposite. It is on such an extreme level that during his first year/s at Hogwarts, some professors wouldn’t believe that James had actually written the essay he handed in, because the handwriting was nothing like what they’d seen from him before. In the later years of his time at Hogwarts, however, both the teachers and his friends could recognize his handwriting, even when it was of a variation they had never seen before. They learned to recognize the things that never changed.
Sirius: extremely neat and tidy, almost painfully so. Each letter is evenly high and wide, perfectly spaced, and Sirius hates it. His mother taught both him and Regulus to write this way, because according her it was the pureblood way to write. She would beat them if their letters ever were not evenly spaced or sized, and even though Sirius tried to alter his hand-writing after running away, he still writes the way his mother taught him. It was too ingrained into his brain to change, and he still winces - expecting a strike - every time he messes up when writing.
Remus: barely readable to anyone but himself. He is always in such a rush to write everything down that it all just muddles into an illegible scribble. The other marauders like to argue that the only reason for Remus’ good grades is that the teachers don’t want to admit that they can’t read his hand-writing so they just give him Outstanding. However, since Remus is so thorough in his school work, not wanting to disappoint Dumbledore, he reads through all his papers before handing them in. In doing so, he notices the words that are just a bit too unreadable and changes it, making it just legible enough. (I also like to think that when he gets older, he either finds or invents a spell to make his hand-writing more legible with magic)
Peter: Very spiky, almost annoyed looking. Peter never enjoyed learning to write, and therefore he didn’t put much effort into it, but when he came to Hogwarts and saw his friends (specifically Sirius’ and James’) handwriting, he got kind of embarrassed, because his own was so messy. So he started putting more effort into each letter he wrote out, trying to make it more tidy looking, but he never really succeeded. He also uses a lot of pressure when writing, so much that his quill sometimes tears up the paper.