Hi there
LDRs generally do not have any specific code or number but yeah they can have generic codes from different manufacturers. LDRs do come with parameter to judge on, you might have seen 5 mm/4mm LDR written somewhere online; this is the wavelength of light to which they are most responsive. Also, sometimes their resistance may vary widely; in dark they offer around 1 Mohm to few ohms in bight light.