Before I went to Chicago (the first weekend) I wanted to make some stickers to use for street art. I found a simple way to make them in a DIY Card Deck a friend gave me a few Christmases ago. All you do is draw the image, scan it in, fix any mistakes, print it out onto label stock, seal with contact paper, cut out the stickers, peel and go.
These are the three types I ended up with.

We didn't put any in the city (sadly),
but we found a place for them on some graffitied rocks.
Soon I'll get braver and put them in the city.