I have a mobile UI element, and I'd like to design it such that users can pull down on it to see more info about that element. Is there a common signifier that says "hey, pull me down"?
as everyone has said... the ubiquitous, traditional, and ever present
down arrow near (usually to the RIGHT of) your default action/button/label text is customary, like so:
What I like to do, if I feel fancy, is have the drop-down arrow/button animate on a hover/touch, before the actual drag down.
So, for instance (although this is not the prettiest example... quick and dirty), you could have the arrow bounce up and down or animate in a downward direction, then reset back and the top, and continue the cycle as long as the user hovers/touches.
Then, once he/she drags down it then actually opens/drops-down your menu, option list, or whatever...
I think the standard icon is the down arrow. A quick Google image search of "down icon" reveals:
That said, I also found this for more of a "pull down" feel:
Generally a small downward arrow is the easiest and simplest way to signify that there is a hidden menu if you click there.
If you want it to be a pull and drag, have it so when you click the button, the menu starts to partially come down and out of it. If they keep dragging, it keeps going down.
If you hate arrows, you can always consider the one time pop up help box that says that instructs the user to drag specific menus.
Hope that helps.