There's a verb, to yawp 'to cry, bark', which is a variant of to yelp. As with many verbs, this, too, has been nominalized (nouned if you'd rather). From there, it is a short hop-skip to adjectival derivation by use of the suffix -ish. That's all conjecture, and tsuwm has suggested elsewhere that it might mean 'noisy, clamorous'.

Ceci n'est pas un seing.