It seems fair to suggest that tigers use facial markings to recognize each other combined with their body scent (odor). In other words, they use appearance and smell to identify neighbors and relatives. This is how humans recognise each other and, in fact, humans use the tiger’s coat pattern to recognise individual tigers.
Tiger coat patterns or markings, including facial markings, are unique to each individual cat. It is believed that the tiger’s facial markings play a role in close range communication.
Scent marks are also used as a means of recognising others. Tigers deposit scent as an odorous musky liquid. It is called ‘marking fluid’. It is often mixed with urine and sprayed. Scent is deposited on feces from anal glands. Tigers rub their cheeks on objects which they have sprayed to enhance the odor.
It is believed that scent and scrap marks convey a tiger’s identity, sex and reproductive status to other tigers.
The white spots on the back of the tiger’s ears may function to signal to cubs to ‘follow me’. This is because in dim light they are visible to cubs trailing behind. The white spots are also used to signal intimidation towards another as the ears are flattened. The domestic cat has the same behavior.
How many stripes do tigers have down their flanks? Here is a chart:
Sources: Wild Cats of the World by the Sunquists and Riding the tiger: tiger conservation in human-dominated landscapes by John Seidensticker.