How Do I Know if Real Botox is Being Injected?

You will never know what is being injected into you. Just seeing the Allergan hologram only means that the bottle you are looking at has a hologram on it.
The fact that you are asking this question means you are not in the right office.
You should choose a reputable physician who cannot afford to give you anything but the best. You will never worry about watered down product or fake product again.

You can visit the Allergan company website to see what the real Botox vial looks like. Better yet you can ask the physician to give you an empty vial and keep it with you to compare in future.
To avoid this issue, its better to go to a reputable physician because its not just the fake Botox you should worry about but also who is injecting it.
Regards

Probably the best way to know your Botox is real is to go to a reputable doctor. But, going beyond that make sure that the bottle your physician is getting your Botox from has a holographic foil stamp. You can find what the stamp looks like on the Botox cosmetic web site.

There have been some senational stories about people getting bogus Botox, and well-publicized prosecutions as a result. I think we are at the point where no medical professional in the U.S. is likely to risk their license by using something else. On the other hand, there was a case near Seattle where a non-medical person working in a beauty salon was injecting bogus Botox and something she told her patients was Restylane, all illegally imported from China. So my advice is watch out for deals that seem too good (Botox is expensive) and make sure it is a medical facility with the responsible physician's name clearly evident.

You are wondering if you are getting Botox when you are told that is what is being injected. You can certainly ask to see the bottle, but I would recommend that you are having it done by a physician, and you should have trust in that physician. If you are asking about the validity of what you are told, then you don't have enough trust in the provider you are having treat you. That may be a concern. You can check out the doctor's references by asking other doctors.

You could go to BOTOXCosmetic.com and check to make sure your physician is a provider. Looking at the bottle or package may be helpful as well.
I hope this is helpful for you.