The WBC to platelet ratio is not a commonly used index in medicine, and does not have any general significance. For example, infection, hematological malignancies, or solid organ tumors can all cause low or high WBC and low or high platelet count .
There is one study  looking at a specific population (patients undergoing splenectomy for trauma) showing that a lower platelet to WBC count ratio can be helpful to differentiate patients developing an infection from noninfected patients. The rationale behind this is that trauma patients often have a high WBC count (leukocytosis due to stress demargination of neutrophils), such that the WBC count is no longer reliable as an indicator of infection. Therefore, this study combined the WBC count with the platelet count, which initially goes down in most patients with infection , to try to improve discrimination between the two conditions. The generalizability of this index is extremely limited since the patient population studied was quite specific.
There is also one study  that showed that platelet-to-lymphocyte ratio (note that lymphocyte count only represents a subset of WBC count) correlates with prognosis in patients with gastrointestinal stromal tumors.
Other than these two studies, a search of the medical literature reveals no mention of the WBC to platelet (or platelet to WBC) ratio.