***** Reviving a thread from 2013 for future reference. *****The fiscal stamp posted by OP appears to have a postal cancellation for ENE 3?. This might be ENE 37, or January 1937.
Soon after the outbreak of the civil war, there was a shortage of postage stamps in the parts of Spain that were under control of the military insurgents. The Fábrica Nacional de Moneda y Timbre, however, was in the zone that remained under the control of the republicans. On 9 November 1936, an order was issued by the insurgents that, provisionally, allowed the use of certain fiscal stamps for the franking of inland post. The order was published in the Official Bulletin of the State (B.O.E.) on 13 November 1936. The use was allowed until the normalisation of the production and distribution of postage stamps.
A further order was issued on 21 July 1937 that required the administrators of Correos (the Post Office) to only allow stamps for the franking of post that were intended for postal use, after three days had passed. Consequently, between 9 November 1936 and 24 July 1937 certain fiscal stamps were valid for (inland) postage.
The use was condoned between 25 July 1937 and 24 July 1939. Examples of postal use are known as late as 1950.
The stamps concerned include that posted by OP and are

If, indeed, the cancellation is for ENE 1937, this, likely, is an example of authorised postal use. If it is ENE 1938 or ENE 1939, it may still be postal use.
Source: El Correo en Canarias. «Correo de Necesidad», Día 23 de octubre de 2022.
Autor: D. Agustín Alberto de León. Presidente de la Federqción Canaria de Sociedades Filatélicas.