First of all, no apartment complex, for sale, is going to advertise their vacancy like the sign above. Why? Vacancy is any units that are not occupied. Obviously this means less rental income.
So should you avoid properties with vacancies?
Not necessarily. If the property's price is based off of the income it makes (See Cap Rate), you may be able to get the property for a discount. Sometimes the units may be vacant because they are in need of repair. This would allow you the opportunity to fix the units, get the property fully rented, and quickly increase the value of the property.
This is a continuation of a serious entitled: The Top 10 Terms of Commercial/Investment Real Estate.