Indeed, fonts are not embedded in ebook formats, so the font used will be whatever the reader has set for the e-reader. (Ebooks can embed fonts, but to do so the publisher of the ebook must own the necessary licence for the fonts - so you cannot just embed a font you have on your computer, but would need to pay potentially thousands of pounds for a licence.)
That said, most e-readers to support a difference between true-type and monotype fonts, so what you could do is uses a monotype font such as Courier instead of a sans serif font to mark the text out as looking different.
All the best,
Keith