For many years scientists have studied our own solar system and modern technology allows them to look deeper and deeper into space. Knowing the Sun is only one of a few billion stars in the Milky Way galaxy, I can imagine scientists also started studying other solar systems… at least enough to know how many solar systems reside in our galaxy. Is there any information available that would be able to (at least "indicate") how many solar systems reside in our galaxy?
A good, but hard question to answer - as you stated, only an indication could be provided. But, there is some information available from the number of exoplanetary systems found 'locally', according to the NASA web page How many solar systems are in our galaxy?:
Another estimate from the article 160 Billion Alien Planets May Exist in Our Milky Way Galaxy (Hall, 2012), particularly with their quote from a scientist:
An important caveat from the NASA site is that exoplanetary observations are still in its infancy - so over time, this estimate is likely to improve.
According to observations by the Kepler space telescope and other ground based observations, it seems that about 5% of the stars in our galaxy have giant gas planets, similar to Jupiter (but often larger). Smaller planets are difficult to detect, but it is estimated that 40% of the stars have small planets orbiting them.
All in all it is said that on average, 1.6 planets are orbiting each star. So almost all stars form a kind of solar system with planets. However, there is still a lot of uncertainty regarding the numbers, since small planets are very, very hard to detect. And other aspects of solar systems, like our asteroid belt, Kuiper belt and Oort cloud are hard to detect even in our own solar system.
But my own opinion is that it is reasonable to assume that we live in a pretty average solar system (because the odds are obviously suggesting this). So I think that almost every star will have a solar system with a couple of planets, some rocky, some gas giants, plus stuff like comets, asteroids and so on.
Source: Wikipedia Extrasolar planets