This is true. The first thing I would think of would be a round 'cartoony' cloud like the ones shown. You could do a more stretched or jagged looking cloud, bu

This is true. The first thing I would think of would be a round 'cartoony' cloud like the ones shown. You could do a more stretched or jagged looking cloud, but it could easily end up implying 'danger' or 'bad-weather'. The rounded happy-cloud does seem the obvious first choice.