An interesting sub-language of Estonian is Estonian Sign Language. This is used by about 2000 deaf people for whom it is the first language, or the primary means of communication.
Estonian Sign Language (ESL) differs from other sign languages primarily in signs, as opposed to the grammatical structure (e.g. the sign for 'pain' in American and Estonian sign language). However, many signs in various sign languages also resemble to each other due to their iconicity. This kind of similarity (about 40 per cent of all signs) makes the message to a large extent understandable to deaf people of different nationalities and facilitates the communication between them.
At the same time, ESL (as many other sign languages) is heavily influenced by the local spoken language. For instance, some signs are expressed by images formed with fingers, which represent the equivalent to the first letter of the Estonian word (e.g. the sign for restoran 'restaurant'), or a method used in oral articulation instruction (e.g. the sign for mahl 'juice' - refers to the strong current of air that is aspirated during the pronunciation of Estonian 'h').
In its formative stages, Estonian Sign Language has mostly been influenced by the Russian and Finnish sign languages (e.g. an Estonian sign for 'butterfly' has developed from the Finnish sign for 'bird').
The most original amongst the 'dialects' of Estonian Sign Language is thought to be the Pärnu variety.