Latvian license plate: Trial (documented since 2010)

Format, years and the law

Format: IZM999, for example IZM674 (9 any digit)
The format above follows the issuing rules: a registration that fits it is one this series could have issued.
Years issued: Documented since 2010; the format is likely older than the first year documented. Still issued.
Vehicle class: Dealer: trade/garage plates bound to a business, not a vehicle. Issued for car, van, truck, bus, motorcycle, and trailer.
Colours: Characters #000000 Background #FFFFFF
Size: 520 × 110 mm · every country's size
About this plate: THE TRIAL/EXPERIMENTAL PLATE (izmēģinājuma numura zīme). Flagged rather than forced. Its fixed IZM prefix makes it the most unambiguous mark in the Latvian system.

7. pielikums 4.3.1-4.3.2; punkts 13.3 https://likumi.lv/ta/id/222145-transportlidzeklu-registracijas-noteikumi

The series id is lv-trial. The API returns its format, validation, colours and designs with the rest of Latvia's series:

curl -s https://vehiclesdb.com/api/v1/plates/lv \
  -H "Authorization: Bearer $VEHICLESDB_API_KEY" \
  | jq '.series[] | select(.id == "lv-trial")'