How to add 5% Gaussian noise to signal

I am trying to add 5% Gaussian noise to the signal.
I created noise like this way.

mu, sigma = 0, 1
noise = np.random.normal(mu, sigma, data.shape)

I am bit confused about this 5% term, is it related to standard deviation.
Or it is like create a noise and add 5% of it to signal.

Or get 5% of the signal and add noise to it.

Can some one guide me how to do this with code

5% of what? I think the way to accomplish it is to set sigma = .05*k, where k is some scalar that you are taking 5% of.