Is there any way to tell if the blue safety cap of an epipen (epinephrine) has been taken off?

Yes: Once the blue safety cap has been removed, it will not be visible on the cap of the pen. If you see the blue cap on the pen, you need to remove it to activate the needle. You want to make sure you inject the orange portion of the epi-pen which contains the needle into the muscle of the outer lateral thigh. The website for the epi pen has a video that can help. http://www.epipen.com/how-to-use-.