Your iPad that shows the number is somehow in service field test mode. On an iPhone you dial *3001#12345#* to get there. Since that can't be done on an iPad who knows how you ended up there...
Anyways, that number is dBm (decibels referenced to 1mW). In real life, you're not likely to ever see about -50 or so. -50dBm is 0.00001mW. Or 0.00000001W. Thus, the reason why all the cell phone cancer worriers are insane.
Also, they love to talk about the absorbed radiation (SAR) from their phones. SAR is calculated assuming maximum transmit power. You're almost NEVER there. I just made a test call on my iPhone. Right now I'm in a call and my received power is -87dBm and my transmit power is 7.30dBm (though that's a real time reading and bouncing around a lot but it's going above and below that a lot), and simply by moving my phone a bit and holding it upright the transmit power fell to -19dBm. That means that I was transmitting in position 1 at 5.37mW and in position 2 at 0.0126mW. The SAR rates are determined transmitting at full power (generally around 200mW/23dBm).
Your Wi-Fi devices run at higher power levels in the real world than your cell phone does. Cell phones use active transmit power control to keep your signal level as low as possible. Wi-Fi will always transmit at a constant level (17dBm/50mW is common) when it is transmitting. Yet, most of the cell phone cancer worriers claim Wi-Fi is less harmful due to the lower power level. Nonsense. Most of the time, the power level of Wi-Fi is much higher. Same with home cordless phones.
How can cell phones operate at such low power levels? The receive sensitivity is amazing. You can be at -113dBm (generally the floor on most UMTS radios) and still hold a call. -100dBm is still perfectly usable and results in good performance. Try that one with Wi-Fi or other ISM band cordless products - your at your noise floor or even below it. Licensed exclusive-use spectrum lets power levels be very low.
Okay, so I guess that's me rambling on far too long, but the point is, that's the number you're seeing and it's very nice to see! Most cell phones show full bars around -80dBm, but often use more than just received power level to calculate "bars" so it's not an exact science. Also, in a dual band market, bars mean even less. For example, in my area AT&T runs UMTS on both 850 (CLR) and 1900 (PCS). If I'm on a PCS channel I can be outside and below -100dBm with just one or two "bars" on my phone, and walk inside a building and get full "bars" and -80dBm or better, because my phone hops onto an 850/CLR channel
To the OP, ignore the bars, they mean very little...