what type of desk decor is this?

i would include a picture but i cant think of what it is so i cant find a picture. its a rectangle shape. the back is all white and the front is transparent. inside it are black squares with white letters on them so you can change the message or line inside. its some sort of desk sign/decor. ive seen a couple people with these one on someones microwave and one on a persons desk and i cant figure out what they are called. if anyone knows what im talking about let me know because its driving me nuts. thanks.