What is a safe and resonable return on investments in the stock market?

For starters it depends on what you are calling the market if you are referring to the S&P 500 then the annual returns have been about 11% for the period from Jan 1, 1975 to December 31, 2006. 75% of mutual fund managers don't beat the index and most investors don't either. If you are projecting out long term returns I wouldn't recommend anymore than 8% or so. You might beat that but you certainly might not. It depends on what you buy if you are willing to hold it, dividend returns and most importantly risk adjusted returns. So picking the index, reinvesting dividends, keeping fees and comissions low you should be able to get better than 8% but nothing is guaranteed.

The stock market has some risk, even for those who know what they're doing. Most financial advisors will tell you to only put about 1/3 to 1/2 of your money in the stock market. Long term rate of return is between 10-15%.

Safe is in the neighborhood of 6.5% up to maybe 8% ( that would be a balanced fund of some sort - heavy in bonds)...but a " reasonable" return would be more like 11% to 15/16%. Which means... some " risk" is " reasonable", so you sort of ease out of the safe category to get a better return.
Plus 4 or 5 percent really adds up over time... so it's reasonable to take that little more risk.
If you get into the riskier investments, you just watch a little closer... if it's worth the effort to you... everyone is different.