Double PCL sign - appears on sagittal MRI images of the knee when a bucket-handle tear of a meniscus (most commonly the medial meniscus) flips medially and comes to lie anteroinferior to the posterior cruciate ligament (PCL), mimicking a second smaller PCL.
Spinnaker sign - a neonatal chest radiograph sign of pneumomediastinum. It refers to the thymus being outlined by air with each lobe displaced laterally like spinnaker sails. This appearance may also be termed the thymic wing sign. Bonus radiology signs also demonstrated in this case include left-sided deep sulcus sign of pneumothorax and continuous diaphragm sign of pneumomediastinum.