The warning symbol is part of the ISO 7010 standard as such its normative in many countries. This standard relies on ISO 3864-1, and ISO 3864-3 for further information about colors and sizes of borders etc.
This probably means at minimum that you lose the unique ability to trademark that symbol. Also while you may in some locales have a copyright on the electronic document you created you will not be able to get others to stop from drawing the same thing again. But most likely you have no copyright.
In this specific case the symbol is ISO 7010-W004. And described as:
Circle with 24 regular equally spaced radiating lines,
12 shorter of equal length, 11 longer of equal length and
one longer reaching horizontally the right-hand side of the
Note the standard does have images for illustrative purposes and many signs use the exact images*. However please be aware that, to my knowledge, the warning signs do not require you to have the exact same design to qualify just fulfill the text in the description field. To this end iso says:
However some degree of graphical modification is permitted when cultural differences or special application formats need to be considered, provided the original meaning is retained and comprehension of the safety sign is maintained.
THis in turn means its extremely unlikely to win any plagiarisation claim in court. More likely your plagiaraising ISO. Because people can just claim to have followed the description in the standard, which is what its intended for.
* ISO claims copyright on them but gives permission to copy them as is (page 1 of ISO 7010:2011).