Show or hide password – icon or textual?

Allowing the user to toggle visibility is becoming a more standardised part of forms, and in my opinion for good reason. I'm however unsure what the best way to denote this ability is; an icon or a togglable label? If hamburgers are already not always recognized, I can imagine that this would be even worse for this feature, especially which status it is currently showing.

My question: is there any research about what works better; a hide/show label or an icon that visually shows the same?