A simple sign has a signifier which denotes its signified; at the second level of connotation, this whole sign becomes a signifier for another signified. Williamson (1978) discusses a series of advertisements for Chanel beauty products which were presented at the time with an image of the actress Catherine Deneuve. At the first level, the advertisement associates the products with Catherine Deneuve, and at the second level, we get the connotations of Catherine Deneuve in the context of beauty products as a signifier: she connotes the classy, chic lifestyle of a mature and sophisticated woman (p. 100).
Indexical components of advertisements typically have connotations, which connect the advertisement to a larger cultural context.
For example, think about the way that hair is portrayed in advertisements for hair products: either immaculately styled, or free-flowing and in motion (look at 43 Aveda or 44 Herbal Essences). The styled image is used in advertisements that connote (a woman, typically) getting herself ready to socialize; the free-flowing image connotes freedom in life: freedom from worries about hair, freedom to travel, freedom of expression.
To take another example, cigarette advertising typically associates the product with different cultural contexts: the wide-open Wild West image of Marlboro is very familiar. Other types of context are quiet, individual settings, or general social fun situations. Compare the Images in 08 Polo and 72 Newport. In the former, the product is placed near some other familiar individual accompaniment, coffee in this case. This Image is indexical for a scene which connotes "a quiet smoke". The juxtaposition of the two objects leads to an identification of the two, and properties associated with a cup of coffee transfer to the cigarettes (see Williamson, 1978, p. 22).