What is unique to the Bikaner School regarding portraits of artists?

Having portraits with information on ancestry

Answer: Having portraits with information on ancestry
The Bikaner School is unique in having portraits of artists, referred to as Ustas or Ustad, and most of them are inscribed with information regarding their ancestry.

The custom of having portraits of artists is unique to the Bikaner School and most of them are inscribed with information regarding their ancestry. They are referred to as Ustas or Ustad. Ruknuddin painted exquisite works in soft colour tones. Ibrahim’s works have a misty dreamlike quality. His figures are dainty with heavily modeled faces. His studio appears to be most prolific as his name occurs on different sets of Baramasa, Ragamala and Rasikapriya. Accounts from the Bahis, royal archival day-to-day diaries, and numerous inscriptions on Bikaner paintings make it one of the best documented schools of painting. Inscriptions in Marwari, and occasionally, Persian reveal the names of artists and dates, and in some cases, even the place of production and occasions for which the works were commissioned.