In terms of communication, smell is used to convey 1) territory ownership and 2) readiness and availability to mate (on the part of the female). Tigers use their personal scents to mark their territory, spraying the local flora with their scent-rich urine. When a female is ready to mate, she will spray her surrounds liberally with her urine, alerting males that pass through her territory and smell her scent that she is ready and willing to conceive. Tigers, particularly females, are territorial, and will mark their territory by means of their scent. Should another tiger enter their territory, they will know that it has already been claimed. Interestingly, the scent identifies its owner as male or female, local or alien to the region.
There are occasions on which these otherwise solitary animals make contact with one another. When this happens, they will be sure to smell one another by way of introduction. During this interaction, a very interesting physical process takes place to enable the tiger to process the odour of the other. The tiger will smell its peer while wrinkling its nose and letting its tongue hang out. This facial expression is called flehmen. It allows for the scent to enter the mouth and be drawn into the Jacobsons organ, which resembles a pouch behind the front incisors. This organ has two tiny openings which then steer the air being inhaled to sensitive nerve structures within. These nerves transmit the odour messages to the brain. This chemical process is a fascinating one. The flehmen grimace has become a trademark of these wild cats, and can make tigers appear as if they are snarling. However they make no sound while contorting their faces and their tongue hangs out rather prominently.
Because tigers are independent creatures that live on their own for the most part, they rely heavily on having effective senses that aid in communication and survival. Their sense of smell is an important asset to them.