How to tell if a piece of metal is really titanium(2)

File or sand off an edge to be sure you are looking at the bare metal. It should be a shiny dark silver. Compare it to a piece of (freshly scratched) aluminum; it should be much darker. If the fresh metal is a different color, then, no.

Does it anodize to color? If you can get to a bare piece of metal, just apply a moist cathode (paper towel) to the positive-attached metal. 9v should do to get a slight tan tinge. 18v (2 9v batteries) will take you to dark violet.
 Note:Niobium and tantalum will color the same way. But they are heavier and softer and more expensive.

If you touch it to a typical rotary hard grinder, the sparks should be bright blue-white.

If you have a way to measure its specific gravity (ratio of weight to volume, water is 1.0 g/cc) then you have another good test.
 Titanium and its alloys range closely around 4.5 g/cc.
 Aluminum is noticeably lighter (2.7 g/cc),
 Iron and steel are distinctly heavier (7.8 g/cc).
 Tantalum is much heavier (16 g/cc).
 Niobium is about the same as brass (8.5 g.cc)
 Copper, bronze, and brass are up to 9 g/cc, but you’ve already eliminated them by color.

If you have samples of steel and aluminum in the same size range, the relative weight is easy to check.

Shavings of titanium (from drilling or milling) burn much as magnesium strip does. Shield your eyes if you resort to this test. btw: Magnesium is much lighter in weight (1.7 g/cc)