Without the maker name there is no standard marking for these kinds of components.
You said batch though, how many do you really have as if you have enough a few additional tests at various current limits can ballpark their intended blow range, depends on how many you can blow in the process.
Personally I'd test them on a programmable power supply and a very slow (like 1 amp per minute) rise in the current going through them. Monitor the temperature somehow and report the temperature at every one minute integral from start along with the current at that point until it blows. That should give you a good idea of generic slow blow trip characteristic, if you look at the datasheet for a comparable polyfuse you should find a maximum safe operating temperature which will give you a standpoint to start from thermally which would be enough to characterize them enough to be useful though you'd need to do a bit more testing to measure their transient response.