A designation is a string that (somewhat) uniquely identifies bots, much like a name does for humans. A designation can also be called a serial number (in name only, for it is neither).

Some formats for designations:

• UUID: e.g. 74ba69db-93c9-465a-8cee-6021f35570bf. Perhaps abbreviated to 74ba or 70bf in casual use.
• symbol-dash-number: e.g. Δ-44203. This format is usually abbreviated to the number, the symbol tends to be dropped in casual use.
• a (hexadecimal) number: e.g. 465A or 0x62656570. As the second example shows, this could be a string represented with Unicode codepoints in hexadecimal.
• a systematic identifier system, like OID or UIC locomotive numbers.

One can come up with a designation by oneself. But it is also fun to ask others to come up with a nice number. (Please try to avoid collisions though!)