some people either make headers/signs in photoshop, or they just play around with different fonts, sizes & colors, like the example you linked. it's honestly just about messing around with things until you like the way everything looks. most people also use animal crossing sprites, but the tumblr that had them all in one big masterpost disappeared. the original site they were found on is here, but it's in japanese.
tumblr is where i get a lot of graphics for my shops, or i just make them myself using paint tool sai or photoshop. i have more control over the overall color scheme and it looks way more unique than using pixels or w/e