Are saying this is a sign from God?
God doesn’t play enigmatic games. If it is indeed of a message from God, as some people seem to be speculating, then God will make sure it is understood. This has been the case at Lourdes, Fatima, and with Our lady of Guadalupe (source: A Still Small Voice: A practical Guide to private revelations by Fr. Benedict Groeschel, CFR).
Assuming this is a sign… What is the message? (If you know what it is, then keep in mind it is a private revelation.)
In this case of the lightening bolt, most people are speculating about a message. Are they receiving a private revelation or are they just guessing? What if all of their interpretations are different? What if their initial interpretation changes after discussing it with others who seem to see a message? Are they all right, or are they all wrong?
And assuming this phenomena is preternatural, the event is supernatural in origin (meaning from God), and there is some sort of message… then…
Keep in mind the words of St . Teresa of Avilla…
I challenge you to read Fr. Groeschel’s book above.