They are Scribbles "dimensional fabric paints", and you're right, they are acrylics, formulated for fabric. They come in little bottles with narrow tips for writing and drawing lines. Unlike most acrylic based fabric paints they don't have to be heat set.
You probably won't find them in the more "up-scale" art supply stores because they are pretty much a craft item. Walmart in Canada has them if you want to look at the bottles. If you buy any, get them here as they're cheaper
This is the brand I use now, but I'll be trying out Artx paints to see if they're as good (right consistency, durability and bright colors) as the Scribbles.