Found this for you: from everymac I'm new here and not too sue if i can post links, so mind the formatting .
Four of the seven iPhone 5s models can be specifically identified by Model Number, which is provided on the back of each phone in tiny type. Unfortunately, the remaining two models cannot be identified by Model Number alone.
Initially, carrier support and distribution will limit the number of different iPhone 5s models that one is likely to encounter in any one location.
However, it still is useful to be able to precisely identify each model, particularly as the iPhone 5s circumnavigates the globe and reaches locations and carriers other than the initial target market.
Specifically, the seven different iPhone 5s models have these model numbers:
As noted above, three of the iPhone 5s models -- two distributed in the US and one distributed in China -- are the difficult ones to identify as they both share the A1533 model number. Consequently, if the iPhone will boot, the most convenient way to identify a specific A1533 iPhone 5s model is with the Order Number -- which Apple refers to as the "Model" within the iOS -- or by the last four characters of its Serial Number listed in software.
To find the "Model" and Serial Number, touch the "Settings" icon on the homescreen and select General > About and then scroll until "Model" or "Serial Number is visible. The "Model" identifier looks like ME305LL, which specifically refers to the GSM A1533 iPhone 5s in gray with 16 GB of storage and locked to AT&T. If the A1533 iPhone 5s is inoperable, you will need to look at the serial number listed within the Nano SIM carrier.