[mothered]

Assuming they drop the box at my porch without a signature (common) and I contact Bestbuy, do they usually launch investigations?

The DNA triggers an Investigation a lot more often than not.

If they require a signature I’ll simply return it… or say it wasn’t my signature, kind of debating.

A signature Is a useless form of delivery verification.

Simply fake sign It.

Is 2 DNA’d from Bestbuy and UPS enough to launch any type of investigation?

As said, the nature of the DNA triggers an Investigation, regardless of the amount you've hit.