I bought a olive green sweater from Walmart for about five dollars and I used orange felt for the letters.
Trying to pick the right font was the trickiest for me. I didn't trust myself to free hand the letters so I messed around on Word to try to find a font that would work.
This picture was before I found the Bookman Old Style font. That's why the font looks different in the next few pictures.
I cut them out and then placed them on the sweater to make sure that size was correct and I liked the way it looked...
Turns out I didn't and used a different font. Anyway, pin the letters onto a piece of felt and cut them out. Pin the letters on the sweater to make sure you like the way it looks. Now would be a good time to try the sweater on.
Okay, now that you waited the right amount of time to let the glue dry, it is now time to sew on the letters! I used a zig-zag stitch and lime green thread. I just sewed around the letters. (I don't really know if there is a better way of doing this but if there is I would love to know.) I went around the letters twice. I found it looks better to sew each detail individually instead of trying to do it all in one pass. (See picture below) This ended up being a lot harder than I thought it would be. Just be patient and take your time with it. It is going to look awesome either way.
Picture below of comparison of different techniques used to sew on the letters.
Now it is time to cut any loose threads you may have and fix any mistakes that were made.As you can see I made a lot of mistakes on the R. I just seamed ripped them out and redid them.
It is now time to rock your new sweater to study Mathematics of wonton burrito meals in the year 3000!
Update: 5/30/13- I'm selling Mars U t-shirts on etsy!