Protect your bottom line. Don’t pick up your pencil until your client has signed dotted line.I refer to temptation for many artists, designers and other creatives to jump gun and begin work on a project before there is a signed contract.
It is not unreasonable to make some quick sketches to outline initial ideas as part of a preliminary discussion. But since anything done at this stage is purely speculative, it is best to limit time spent until there is some kind of commitment by client.
If it is difficult to define scope of a project until a greater amount of preliminary work is done, consider drafting a separate agreement covering preliminary phase.
When you begin work before contract is signed, you are expending your time and skills in expectation that you will eventually be paid. But without a signed contract, client has no obligation to go through with project, make any payment, or assign project to you if he does go forward.
If client himself won’t commit to you, or can’t commit to going ahead with project itself, be wary. You may be dealing with a difficult client.