Here is the piece I read so long ago about ads. It is from the 1800's
need for repetition when advertisting. This was written in 1885 by Thomas Smith: That is not 12 but 20 times seeing an ad. How true it is only testing for each product or service you have can tell.

1. The first time a man looks at an advertisement, he does not see it.
2. The second time, he does not notice it.
3. The third time, he is conscious of its existence.
4. The fourth time, he faintly remembers having seen it before.
5. The fifth time, he reads it.
6. The sixth time, he turns up his nose at it.
7. The seventh time, he reads it through and says, "Oh brother!"
8. The eighth time, he says, "Here's that confounded thing again!"
9. The ninth time, he wonders if it amounts to anything.
10. The tenth time, he asks his neighbor if he has tried it.
11. The eleventh time, he wonders how the advertiser makes it pay.
12. The twelfth time, he thinks it must be a good thing.
13. The thirteenth time, he thinks perhaps it might be worth something.
14. The fourteenth time, he remembers wanting such a thing a long time.
15. The fifteenth time, he is tantalized because he cannot afford to buy it.
16. The sixteenth time, he thinks he will buy it some day.
17. The seventeenth time, he makes a memorandum to buy it.
18. The eighteenth time, he swears at his poverty.
19. The nineteenth time, he counts his money carefully.
20. The twentieth time he sees the ad, he buys what it is offering.