Signing bonuses tend to come and go, depending on the state of the economy. In a tight labour market, when skilled workers are at a premium, it can be a relatively straightforward to ask for one, and your new employer may be happy to comply. When times are tougher and there are more people out there looking for work, it's a harder negotiation.
Do your research. Look on the Internet at sites such as salary.com, or the Bureau of Labor Statistics to discover the average compensation for the type of position you're up for. Ask around among workers already at the company, or your other industry contacts, to see if signing bonuses have been paid recently, and if so, at what level. Signing bonuses are more common in industries such as IT or telecoms, where workers may have specialised skills.
Wait until you have a firm offer in writing before beginning a negotiation. If you jump in too early with the demand before you're offered the job, you'll appear greedy, and you may lose out to another candidate.
Calculate what your expenses in taking the job are likely to be, such as extra commuting costs, relocation expenses, childcare or a spouse's loss of income when you move. These can be very practical and persuasive reasons to ask for a signing bonus
Make a mental list of your unique qualities. Have a ready answer to the question the employer is bound to ask: why should she pay you a signing bonus? List the skills you're bringing to the job that may be hard to find elsewhere. Mention specific things you may be giving up from your old job, such as an expected year-end bonus or maturing share options.
Remember to keep the right tone--you are requesting, not demanding. You should remain professional and cordial, but at the same time be firm and confident.
Sometimes when employers do grant a request for a signing bonus, the company may attach strings. Most commonly this would be a payback clause for any early departure, so that if you leave the firm within a set number of years, you would be liable to pay back all or part of the bonus amount. Make sure you understand and are comfortable with these terms before you agree.