Hi,
Today I made decals for my white jersey : just a few red numbers. I used Inkscape 0.47, some transparent paper decal for inkjet printer, and a cheap HP deskjet f2280 "all in one" as printing device.
I simply write numbers with the text tool, then resize them, and print some normal paper previews.
Once I was OK with the result, color and size, I made some "strips" (I'll make photos once it will be dry) of numbers to save paper space, and to be able to just cut the strip and reuse the decals paper after.
Then, I set up my printer :
"HP presentation gloss paper" setting
"optimal quality" setting
And...that 's all ! I printed the decals, and the results is just so professional

If I was thinking it was so simple and good looking...I'd try it a way before !
Once the paper is dry, I coated it with acrylic mat varnish spray can. Beware, sometime the spray can burn the decals paper, but hopefully, I'm on a good day.
The result was soo good, I printed a little strip of helmet logos too (I founded some open source SVG format niners logo).
Now I believe I'll be able to complete teams painting very fast
TOnight I'll update my niners' topic. Feel free to ask anything. But be sure, it's quite simple, even for a beginner, to make at least his own jersey numbers !