I know that there are notches but from experience I have found that this is not a reliable method for identifying a 3.3V requirement, as almost all PCI cards are notched for Universal insertion regardless of their power requirements.

Can someone who knows which pins are used label a picture to illustrate which pins to look at on the card edge for 3.3V? This would be helpful at a glance to at least identify boards where the pins are completely absent.

I've also wondered if it would be possible to make a voltage "detector" that is a PCI slot on a little board with a battery. It would test continuity across all of the voltage pins and if they are short then a green LED would turn on to indicate that they are all connected. I don't know if this is a reasonable way to detect 3.3V or if these pins would even be connected together. My theory is that if they are dummy pins then they wouldn't have any traces and would not short.

Another use for such a detector would be for there to be a red LED to indicate if the 3.3V and 5V pins are shorted.