....buy what you like and can afford.......
That's the best piece of advice anyone can get or give.
There is no such thing as a sound investment. When I graduated from my post secondary education at the age of 21 my father bought me a brand new house as a graduation gift to help me get started in life. In exchange, he made me promise him that by the time I was 30, I would put away a 100,000 in a retirement savings plan. I did that...a divorce later and market crashes that 100,000 dwindled down to 17,000. I swore, that I would never invest in another retirement plan or stocks after that. 26 years later, that plan is worth around 50,000 and I pay 4000 in administration fee's a year. Long story short, everyone, made and continues to make more money on that investment but me. When I start drawing money out of it...I'll have to pay taxes.
Trust me, collecting signs is much cheaper and carries much less risk and taxes. I will continue to buy and hoard collectibles. Pickers and flippers are probably a lot easier (and cheaper) to deal with then bankers and lawyers!