Visa Signature is the visa that has "no pre-set spending limit", but it does have a "credit access line" which is the normal CL. You can exceed the CL as needed.
I have a Chase Marriott Signature Visa with a CL of $5000. Current balance is $142. Just checked EQ and saw the CL reported as the highest I ever had a balance on there ($2200). Are they pulling a capital one here? Or because it has no pre-set limit it just reports it as 0 like AMEX PIF?
No matter - I am paying off the small balance, putting the card in the sockdrawer, and enjoying the free room night and 20,000 marriott points.