I was thinking of written vowels, not actual vowels. Anything with a stop in it is right out, but as Olly demonstrates, fricatives (and nasals) can be articulated and sustained without recourse to vowels. The Mandarin word for four sz is an example of a word with a vowel. English sss, the sound a snake makes or as a show of disapproval, sh to shut somebody up. Also, English uses clicks, but not as words as some Khoisan languages do. Tsk, giddyup, and kiss are usually articulated as clicks.

Ceci n'est pas un seing.