If you simply upload a file with your logo/name without following the directions on this SmugMug help page  it will appear bigger on the images (depending on the file's dimensions of course). 

For example, if I use my logo without creating a watermark with 1600 x 200 pixels dimensions, it will appear bigger on the images. 

If you would like your name/logo to appear smaller in one of the corners, first, you'll need to create a .PNG file as explained on the referred help page above and position the logo where you want it to appear on the image on SmugMug. So for example, I would like that logo to appear on the bottom right corner and resize it smaller, I'll need to create a file in Photoshop CC, Photoshop Elements or Gimp, like this: 

Then select "Bottom Right" for the Placement: 

If you want the logo to appear in the bottom left corner, position it there in Photoshop CC, Photoshop Elements or Gimp and save it as a transparent file, then upload it to an unlisted gallery and create the watermark, selecting "Bottom Left" for placement and so on. 

Back to main page, explaining the watermarking feature