On 6/9/2020 9:34 PM, Andy wrote:
I have some wood I keep in a closet.

Most is plain untreated 2x4 pine and plywood.

But one 2x4 is marked as follows:

[...]

I want to know if it is safe to keep that one piece in a small closed where the door is kept closed except when retrieving wood.

It is safe provided that there is no overhead lighting in the closet.