This might be a random post, but I still want to pose the question here.

Do you think showing and using your Marriott branded credit card at check in helps with Room upgrades, regardless of Marriott status?

What’s your thoughts or experiences been?

Nope.

No. Only time I’ve ever had a Marriott CC noticed is at the Ritz Carlton Naples Spa (not the check-in).

I truly believe paying with something like the Centurion CAN help but obviously not unilaterally. YMMV

Upgrades are assigned by each individual hotel. Every hotel (even corporate-owned and operate ones) are separate businesses. Since hotels receive nothing when a guest signs up and/or uses the chain's credit card, they aren't going to care what type of card a guest uses.

I have no direct knowledge about the Property Management System (PMS) used by Marriott. But, none of the various PMS I've seen provide information on which bank issued a given credit card.

In that scenario, the only way a Front Desk staff member would know you are using a chain-branded credit card is if you physically hand it to them (and they look). Or even less likely, the staff member would have memorized the common sequence of numbers for the card. (I want to say that the first 7 digits of a Visa/Mastercard can be used to identify the issuing bank. But, it's been a minute or two since I've needed to know that information, so don't quote me.)

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TL;DR: The likelihood that using a chain-branded card will help with an upgrade are close to zero.

At several different Ritz Carlton properties I've had FD agents mention that I get a folio credit for using my Chase RC credit card. These were without actually handing them the card. The credit is simply a benefit of paying with the card, and is not associated with the reservation or room rate.

So there may be some way for properties to tell in advance if a particular branded card is on the reservation. However, I have no idea whether the CC made any difference in upgrade success at those properties.

Are you talking about the $100 property credit perk for the RC card and Bonvoy Brilliant at Ritz and STR properties? If so, that credit is attached to the room rate. If not, I'm curious to hear more about the folio credit.

These types of credits happen at the reservation level, so it simply appears on the reservation when pulled up on the PMS. I do not know of any hotel PMS that shows the cobrand of the card used.

The only common situation where FD staff are trained to check for the card is stuff like FHR where the room rate is required to be paid using an AMEX.