I may be reading too much into this, but I have an opinion question for you all. I did a candle spell to bring someone back to me. This person is in a relationship that isn't going so well. I did a vinegar bottle (then felt bad for having done something so negative) so I cleansed my house and myself for protection and then lit the candle and did the candle spell to bring the person to me. The candle burned out and I went to bury it. I set it on the counter by my back door and, a pan in a drying rack fell over and knocked it onto the floor and it shattered. It could be a coincidence...but I almost felt as if it was a sign that they were going to "break" up. Opinions on this?
To me, the jar breaking doesn't seem like the way you interpreted, but rather a way of the universe sort of..."undoing" your spell. Attraction spells can be very powerful magic, and when it's used in a situation when it may not be meant for the person to come back to you, then there could be negative consequences. I think that when you acknowledged you did something negative, the universe responded by the shattering of the jar to break the spell.
In other words, signs of the spell working wouldn't include the breaking of a container that you manifested your energy in.
As many people will tell you, though, any omens or signs are largely up to the interpretation of the caster. So, whatever you felt may be what it is. It's just seems to me a sign that wouldn't normally indicate success.