There's a huge problem in the world of graphic design in terms of how those designers are being taught or, at least, where their focus is in the design process.
What many of us on the production side for branded products (e.g. signs, displays, promotional products, printed marketing collateral) are seeing are logos and graphics being designed for web purposes with no thought being given to the best possible outcome when those logos are used in the real world for physical items.
In light of this, here's a very basic primer on what those of us who have to use logos and graphics need to make them look their best when we're producing your tangible items:
- Vector files are always preferrable to bitmap/raster files because they can be sized up or down at will with no loss of clarity and no risk of pixelation. These files are most commonly ai, cdr, eps or pdf formats. Just beware that a bitmap file isn't embedded into one of these file types as that doesn't magically make them vector files. (SVG files are vector, but specifically meant for online use and don't always work well as pure vector files like the other formats.)
- If a bitmap/raster file is absolutely necessary due to inclusion of photographic images or gradient images, it must be created at the size it will be printed at and at 300+ dpi for most purposes. Some large format signs can be saved at 150+ dpi and, if large enough, even 72+ dpi. Taking a smaller file and enlarging it will only result in pixelation, know matter what dpi the original started at.
- The color models used for physical items is either CMYK or PMS (Pantone Matching System). CMYK is more variable in getting exact color matches while PMS is an exact color matching system and often referred to as "spot colors." CMYK is based on the same technology used in your home color inkjet printer - four inks (sometimes a few more are included in professional level equipment) to achieve the full color spectrum. If you're using the RGB (red, green, blue) or Hex color models, those are specifically for monitors; not for real life products.
Finally, if your graphic designer doesn't understand all these terms, you need to consider whether their depth and breadth of understanding of graphic design will meet your needs without causing you undue expense to get their creations converted into usable formats down the line.