Having a Visa signature will not help your utilization unless you intentionally stack a high balance for once. However, a Visa signature is a very reputable card. Under manual review, underwriters know that the limit on the card is at least 5,000, and that the credit quality of the borrower is at least very good.
Plus they can always (manual or otherwise) factor in any debt from your flexible spending credit card into your overall debt:income ratio (although this should hopefully not be significant).
Now what would be interesting is if somebody managed to get a large transaction to post (in some excess of the credit limit) on a Signature/World card that didn't report CL to the bureaus. My understanding is you are meeting your obligations if you PIF the amount in excess of your credit limit after it posts. OTOH, if they ever decide to start posting the limit, you'll have a high balance higher than your CL, but a) I think systems will recognize the flexible spending credit card and b) I had a high balance of 10% and 3% in excess of my CL on the two cards I had when I applied for a CSP (~10% util at the time, of course) and they didn't seem to mind.