Glossary entry (derived from question below)
English term or phrase:
insurance stamp
Spanish translation:
contribuciones/aportes a la seguridad social
English term
Spain
Legal and financial translations
Native in: Spanish (Variant: Standard-Spain) 
, Galician
Works in: German to Spanish, English to Spanish, Portuguese to Spanish, and 5 more.
insurance stamp
cheques, giro cheques, bankers drafts, national giro drafts, money orders, postal orders, stamp franking machine units, national insurance stamps, national savings certificates, credit sales vouchers and value added tax purchase invoices (insert limit) for any one Occurrence
| 4 +1 | contribuciones a la seguridad social |
Claudia Luque Bedregal
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Jan 17, 2013 17:33: Claudia Luque Bedregal changed "Edited KOG entry" from "<a href="/profile/112901">Andrés Barral's</a> old entry - "insurance stamp"" to ""contribuciones a la seguridad social""
Proposed translations
Italy
Accurate translations
Native in: Spanish
Works in: English to Spanish, Spanish to English, Spanish, and 5 more.
contribuciones a la seguridad social
http://www.collinsdictionary.com/dictionary/english/insuranc...
(administration, British) an insurance contribution
http://oxforddictionaries.com/definition/english/insurance+s...
British
a stamp which certifies that a weekly payment has been made towards National Insurance:
he had to pay sixpence a week for his insurance stamp
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Note added at 58 mins (2013-01-06 23:47:40 GMT)
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http://en.wikipedia.org/wiki/National_Insurance
(...)
The current system of National Insurance has its roots in the National Insurance Act 1911, which introduced the concept of benefits based on contributions paid by employed persons and their employer.[3] The chosen means of recording the contributions required the employer to buy special stamps from a Post Office and affix them to contribution cards. The cards formed proof of entitlement to benefits and were given to the employee when the employment ended, leading to the loss of a job often being referred to as being given your cards, a phrase which endures to this day although the card itself no longer exists.
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Note added at 16 hrs (2013-01-07 15:31:39 GMT)
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Efectivamente como dice Noni, es algo muy antiguo y ya no existe. Yo he propuesto traducirlo como "contribución/aporte al seguro social" porque me parece que da la idea de lo que fue el "national insurance stamp", pero otra opción válida podría ser "cuotas a la seguridad social".
También podrías utilizar la explicación de Noni, es decir usar "cupones", sobre todo si la traducción de tu texto es para España.
Discussion
En España, utilizamos (si no está domiciliado, es decir, pagable por vía electrónica) unas hojas que se llaman *cupones* que son lo que se presenta si vas físicamente al banco para pagar la cuota. Con el sello mecánico del banco sobre ese cupón, tienes prueba de que está pagada.