idk what that program you linked to is, but there's another method you could try? anyway go to this site:
http://www.thulinma.com/acnl/
1) under load ACNL file load up a QR design that YOU made. it doesn't matter if it's just like... a random doodle. it just needs to have your info on it.
2) click the copy creator button.
3) upload a picture with the qr in it of the sign you want. Since you have 4 just upload one of them at a time.
4) click paste creator.
5) scan the qr code with your 3DS, and now it should let you put it on the sign? you'll be able to edit the picture in game as well.
hope that makes sense??