Frame synchronization is conventionally intended as "epoch recovery" of a symbols synchronous stream. But, what happens when symbol timing is unknown? A typical approach to this problem involves oversampling, which is computational intensive. This paper introduces a novel alternative approach whereby the detector is made aware of the emerging ISI due to imperfect symbol timing recovery in order to achieve the wanted performance with low computational complexity. The resulting sequence, identified as ISI-UW, is obtained as the combination of several conventional UW appropriately shifted in time. The adoption of this particular sequence structure allows to enhance performance in the worst case scenario, at the cost of a slight performance loss in the ideal case, and reveals to be an interesting low-complexity alternative to conventional oversampling techniques to cope with symbol timing fractional misalignments.