The following (or something like it) should be added to power.py before `def _eval_is_real`

```
    def _eval_is_imaginary(self):
        if self.base.is_negative and self.exp.is_Rational and not self.exp.is_Integer:
            return True
```

Then

```
>>> eq=(sqrt(-625 + 29*sqrt(5))*sqrt(-5 + sqrt(5)))
>>> sign(eq)
1
>>> eq=(sqrt(-625 + 29*sqrt(5))*sqrt(5-  sqrt(5)))
>>> sign(eq)
I
```

hmmm ... is that right, sign(I)==I?