Help with Graphic Design - Does anyone know what tool is used for this?

Almost looks like a grunge based typeface or font. Though, I understand it could easily be an effect filter too. 

You can do it like this

Start with a Grayscale document, and add your shape. Rasterize that layer, fill with white using Behind mode, and convert it to a Smart Object.

On this SO, run the Gaussian Blur and Color Halftone. The great thing about this is you can update the filter values later, if desired. Add a Gradient in the Smart Filter mask if desired.

It's a halftone filter, possibly a halftone filter masked (so the top half is not halftoned)
You can either apply the filter to the mask, or to the letter duplicated and mask out the top area to reveal the original layer.

I would suggest trying the Filter>pixelate>colour halftone (even if it's not in colour) and play with the numbers.

A good explanation here.

https://www.makeuseof.com/halftone-effect-in-photoshop/

My method would be to get a halftone pattern somewhere and use it as a mask for the M. That way the effect is not dependant of the colour, or lack thereof) of the original shape, and you could use it on a piece of text, instead of having to rasterise/outline it when using the filters (but that's just me). But it wouldn't necessarily "follow" the shape as in smaller points inside the sahpe, bigger outside)

Now you could also use the halftone filter in the filter gallery, but it would only work if you got more than one colour, Another way would be turning your image (assuming it's in RGB/8) into "bitmap" which simulates halftoning (You'll have to play with the numbers there and go to image>mode Grayscale - then same menu and "bitmap).

So many ways!

PS: Personnaly I think it's done with Illustrator, but since you asked in the Photoshop forum 🙂