In the Name of Allah, the Inspirer of Truth. Assalamu Alaikum Warahmatullahi Wabarakatuh
definition of E120: E120 Cochineal, Carminic acid, Carmines, Natural Red 4 [Colouring] [possible allergic reaction] [animal origin] Source: www.bryngollie.com Cochineal: A red dyestuff consisting of dried bodies of female cochineal insects
If you have a product which contains several colours including E120, (like smarties pink and purple) then (in my opinion) as a matter of caution, it is better to abstain from this product. The reason being is that when handling the sweets, the body heat cause the colouring to become wet and there is the risk of the Haraam colouring spreading.
That said, Nestle do not consider Smarties suitable for vegetarians.
And Allah knows Best Wa Alaykumussalaam Wa Rahmatullahi Wa Barakatuh www.foodguide.org.uk