Original Message

Sign on bonuses are just that, a sign on. Doesn't mean they're higher on the step scale than you. I remember a guy who interviewed with me at rotorcraft back in 2012 just to get the offer, then countered his employer "westwind" and they matched the rotorcraft offer so he stayed. 

Fastforward 5 years later, I'm at Westwind and got hired on about 10k a year more than the 2 most senior pilots. But this is just one example of a bad company.

Having a publised payscale with steps makes it a honest playing field. At this point, if someone else is offering more salary elsewhere I say make the jump. Unless you aren't replaceable (which you are), I doubt your employer will care in the end. It's a numbers game both ways. 

-cheers