Let’s assume that you found or are given a metal piece, strip, sheet, rod or wire that you hope is titanium. Titanium can be many colors, and it might have any number of coatings. I’ve received titanium covered with rust, that transferred from a piece of steel in a wet shed. I have some titanium now that has a tenacious ceramic-like coating that conducts electricity, and is a bear to grind off. I had to get it all off of a piece to do and anodizer test.
How do you tell if it really is titanium?
First: Titanium is non-magnetic. If a magnet sticks, then no. I always carry a neodymium magnet for scrap yards and estate sales.
Are there any grade markings on it? If so, there are many that might mean titanium in its many grades and alloys. Most alloys can be anodized. I usually Google the numbers to see what variation of what grade I find in scrap yards. Many different specifications exist for chemically/commercially pure titanium, depending on sub percentage trace elements (mostly oxygen) and what certifications it has received (mil-spec, medical, etc).
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).
The Mrtitanium Forum 
Thanks for taking the time to write these down! I didn’t realize there were so many ways to tell.
I have a question you may be able to help with (you seem to really know your stuff)!
My wheelchair is titanium and the frame has some pretty deep(ish) scratches on it. What’s the best way to get these out, that wont make the area really shiny?
Thanks!
Hiding the scratches depends on the texture and color of the finish. You can get a brushed metal finish with steel wool, or a 3-M scrubbing pad, or a wire brush wheel. There are many alternative ways to finish a surface, and what techniques to use depend on the result you want.
That’s way more clever than I was epetxcing. Thanks!
If you have a fairly accurate spring balance, you can hang the piece of metal from it and weigh it in air, and then completely submerged in distilled water. From that you can work out the density of the metal. I won’t explain how, but it isn’t particularly difficult. Archimedes did this thousands of years ago, and his technique got a goldsmith executed, because he proved that the smith was mixing gold with silver and charging the king for pure gold.
This is an aside to the Specific Gravity paragraph, one of the ways to get the number. Here is that procedure.