See more: Research
In 2011, Anne de Meijer (NL) tested whether (non-signing) hearing children (6-8 years old) find it easier to remember iconic signs, compared to non-iconic signs.
After 1 week, both reception and production of the newly learned signs were tested. Overall, children scored better on iconic signs.
Click here, to read the report (in English).
There is evidence (source?) that adult learners learn to UNDERSTAND iconic signs faster, compared to non-iconic signs. However, adult learners will make more mistakes in the PRODUCTION of iconic signs. Learners focus on the meaning of the sign, and do not process the exact handshape(s), orientation, movement, etc.