The important point is whether the mark is being abused as a false indication of the origin of the goods. In the case of UA strings this is plainly not the case (now). Vendor IDs are still considered to be indicative of the vendor - such an objection could be avoided by a disclaimer but this may yet not be enough if vendor-id were the common method to determine origin.

Of course their are rules against using as a TM something that is not indicative of origin (generic names of products &c.) and so if a name were needed for interoperability purposes then it could well be argued for free use.

I perhaps trolled slightly. Mea culpa.

As for Chrome browser identifying as Safari, I think not, what does Help > About say.