Where I'm from (UK) this has always been called the "hash" symbol. Although British Telecom voice prompts insisted on calling it the "square" key for a while.
To hash means to chop up, which is a possible origin. To [cross] hatch means to colour in a space with [crossed] parallel lines, which is also possible.
To hash means to chop up, which is a possible origin. To [cross] hatch means to colour in a space with [crossed] parallel lines, which is also possible.
(I know you know this. Others probably don't.)