Find the nearest lead shielding to hide from radioactivity
If I came across it, I'd wipe it off and apologize.
I know exactly how I would respond to such a sight. Excited, elated, curious, and would observe until I felt it might be safe to approach. What a wonderful thing to have happen whether good or bad. However, I think our first contact, if there ever is one, will be a probe, possibly a Von Neuman machine and even that could be good or bad.