There should be a part number on the diff, maybe the ratio is possible to check with that?
Of course it`s always possible to count the ratio by turning the driveshaft connector (???) and checking how many turns it takes to turn the outgoing thingys (ie. wheels)
No marking will be on the hypoid casing. Std housing to suit various crown wheel & pinion ratios.
Apart from identifying the date of vehicle manufacture / vin no & therefore the ratio, the only other way is to measure the ratio yourself
Take one piece of chalk & mark the input flange (pinion) at 12 oclock.
Now mark the output flange at 12 oclock or insert a halfshaft & mark that.
Somehow, you will need to secure the hypoid on a bench or someone must hold it down
Using a tool to turn on the output end, turn the output flange one turn.
Someone with you can count the number of each turn the input flange makes, then using a dial gauge measure the percentage of the last turn the input flange makes, ie .68 or .72 of a complete input flange turn.