The two signs are an example of lexical variation. Both signs are high on the iconic scale. The sign used by older signers refers to a timepiece that was worn on the wrist and that could be heard ticking. The sign used by younger signers also refers to a timepiece worn on the wrist but with no reference to the sound, but to the two columns shown on a digital watch. It is not always the case that a sign used by a younger group will be taken over but in this case, the iconic reference to a more modern technology is likely to lead to change.