A swollen leg is easy to explain away as the end of a long day. That habit is the mistake this page is meant to interrupt, for readers in Tinley Park, Illinois who have had a clot before or who worry about one.
What one source lists
www.nhlbi.nih.gov names this sign: "Swollen and tender legs that are painful to the touch, if you have blood clots that block blood flow to your leg veins ( deep vein thrombosis or DVT )". The sentence ties swollen, tender and painful legs to blood clots that block flow in the leg veins.
What you can do alone
Reading is safe to do alone. MedlinePlus has a page on blood clots for general background. You can also note which leg is affected and when the change began, so that you have plain facts ready for a clinician.
What stops home judgment
Nothing on this page lets you rule a clot out by looking at your own leg. A leg that is swollen and painful to the touch is a question for a clinician, not a puzzle to solve with a mirror and a guess.
One more name you may meet
There is also a Society for Vascular Surgery page on May Thurner Syndrome. It is listed here as further reading for the curious, and it does not change the advice on this page.
The conservative choice
If you are unsure, treat the leg as a reason to ask. The sign that should change a wait-and-see plan is the one already described: swelling with tenderness or pain on touch.