ESB ready to keg?

I am almost ready to keg an ESB I brewed nearly a month ago, but I don't have a hydrometer to measure the FG (I will be getting one next time I go to the store, but probably won't make it before it's time to keg). I'm wondering if it's possible to tell when the beer is ready to keg by how it looks-- for most of the secondary fermentation, there has been a ring of tiny bubbles along the top of the liquid level in the carboy, and these bubbles have been decreasing in number for the last few days to the point that there appears to be very little yeast activity. In the absence of a way to exactly measure the FG, does this indicate that it's time to keg the beer?

Taste it!

i've always wondered how to go about doing that without contaminating the beer (in case it needs a few more days, I don't want to let any wild yeasts get in...)

After this long I wouldn't hesitate to keg it.

I recently kegged a month old ESB. I dropped from 1.065 to 1.011 sometime during those four weeks. I'm confident it was within the first two weeks.